Rhubarb Crisp Recipe

A sweet 'n' sour rhubarb crisp, with a hearty brown sugar/oatmeal streusel topping.

20170414-rhubarb-crisp-vicky-wasik-4.jpg
Vicky Wasik

Why It Works

  • Whole wheat flour gives the streusel a graham cracker–like flavor.
  • Anise seed and Chinese five-spice powder complement rhubarb, coaxing out more of its natural aroma, while cinnamon adds earthy depth.
  • Tapioca starch forms a light, clear gel that keeps the filling gooey and thick, never gloppy.
  • The sweet and complex aroma of elderflower helps open up the floral notes in rhubarb.
  • Baking in stages creates the ideal ratio of gooey filling and tender fruit.
  • Baking soda mellows the sharp acidity of rhubarb, lessening its sometimes chalky mouthfeel.

Rhubarb seems to divide folks along lines of love and hate, but I often suspect the haters may have once been traumatized by a bowlful of overcooked rhubarb mush. Yet even when it's perfectly cooked, rhubarb's high levels of oxalic acid can sometimes create a tooth-coating chalkiness that would leave a bad taste in anyone's mouth.

Oxalic acid is the same culprit behind the dreaded sensation of "spinach teeth" after a salad, and it exists at toxic levels in rhubarb leaves, so be sure to toss those out! The high but tolerable level in the rhubarb itself leads some bakers to bury their rhubarb in sugar, which makes for a painfully sweet/tart concoction.

With all those pitfalls, it's no wonder some folks are on the fence about (or outright hostile to) rhubarb, but happily those problems can all be solved with science and, perhaps, a dash of artistry when it comes to seasoning. And for those of us who already love rhubarb? These tricks will take that passion to the next level.

Close-up of pink and green rhubarb stalks

The first step is to make the streusel topping, which is what makes a crisp a crisp. Compared with a pie dough, streusels are much more forgiving, making it easy to swap one recipe for another. So if you've got an old family favorite, feel free to use that instead. While there's a "master formula" in my cookbook for making and customizing streusel for any recipe, this is the specific combo I like to pair with rhubarb.

It's a mix of brown sugar, whole wheat flour, and rolled oats, with cinnamon, anise seeds, and Chinese five-spice powder. Plus butter—lots of butter—to enrich the otherwise lean fruit filling.

Whole wheat flour gives the topping an extra-crispy sort of texture, combining with the brown sugar and cinnamon to create a graham cracker–like flavor, but if you don't have any on hand, all-purpose will do. If you're gluten-free, just grab your favorite APF-style blend.

The aroma of anise seeds (along with the echoes of fennel and star anise in the five-spice powder) works wonders with rhubarb, coaxing out more of its naturally herbaceous flavor without overpowering its delicate taste—an idea I picked up from one of my favorite books, The Flavor Thesaurus.

Like adding a pinch of nutmeg to béchamel, a bit of ground cloves to banana bread, or a dash of coriander to my blueberry pie, using this spice combo isn't about making the spices stand out; it's about underscoring the main attraction, somehow making the rhubarb seem rhubarb-ier. If you like, the streusel can be made in advance—it'll keep for about a week in the fridge or a few months in the freezer.

Chopped raw rhubarb segments on a wooden surface

If you've read up on my game plan for making the best cherry pie, my formula for thickening a rhubarb crisp looks about the same on paper, although the method itself differs in a big way (more on that in a bit).

Start with the weight of the prepared rhubarb—in this case, 44 ounces—then add 5.5% tapioca starch and 25% sugar. (This math is all much easier if you work in metric units, by the way.) The numbers in my recipe are rounded for convenience, but the percentages are handy to know if you'd like to scale a batch up or down depending on your farmers market haul.

Now, here's where things differ from my method for pie. The unique format of a crisp allows me to bake the fruit in stages, instead of tossing everything together, topping it with streusel, and baking it all at once.

I start by combining half of the rhubarb with the sugar and starch, plus two ounces of elderflower liqueur, such as St-Germain. If you don't have any on hand, you can use water or an extra two ounces of fruit (rhubarb is about 90% water), but the delicate floral aroma of elderflower goes a long way toward opening up the subtleties of rhubarb.

Collage of making filling for rhubarb crisp: pouring sugar and tapioca starch onto chopped rhubarb, rhubarb coated with sugar and starch, coated rhubarb in baking dish, rhubarb after baking

Transfer the mixture to a seven- by 11-inch baking dish. (A deep-dish nine-inch pie pan will work as well, but I prefer the rectangular shape to maximize surface area for the streusel later on.)

Cover the dish tightly in foil, and bake it until juicy. This takes about 30 minutes in a 400°F (200°C) oven, although the time can vary quite a bit depending on the dimensions and material of your baking dish, so check on the fruit a little early if you're using a metal dish.

Once the rhubarb has given up its juices, pull it from the oven and stir in a quarter teaspoon of baking soda using a heat-resistant spatula. It's not enough to fully neutralize the rhubarb's acidity, but it certainly takes off the sharper edges—a particularly helpful trick when you're working with hothouse rhubarb, which can taste especially sour. Spinach teeth, begone!

Chopped rhubarb in a baking dish, surrounded by a foaming liquid

Keep stirring until the fizz dies down to ensure no pockets of baking soda remain unactivated, then pour the syrupy rhubarb over the remaining rhubarb. Fold gently to combine, then return to the baking dish.

Baking in stages produces a variety of textures in the finished crisp, with creamy pieces of rhubarb melting into a gooey filling alongside big chunks of firmer fruit. Top it off with the prepared streusel, smashing each handful into a thin sheet.

It may look a little strange, but this keeps smaller crumbles of streusel from falling down between the pieces of fruit and sinking into the filling; the "tiles" stay perched on top, where they can bake up nice and crisp.

When the whole thing's covered, return it to the oven, and bake until bubbling-hot even in the very middle, about 30 minutes more.

A finished strawberry-rhubarb crisp in a blue ceramic baking dish

This ensures the tapioca starch can do its thang. If it's not bubbling-hot, the filling won't thicken as it should, so let that be your cue rather than any strict timetable.

Again, the exact size, shape, depth, and material of your baking dish will play an enormous role in how long this process will take. Larger pans, or those made of metal, will require less time in the oven, while smaller or deeper pans may require quite a bit more. You can absolutely bake with whatever type of pan you have on hand; just let your eyes be your guide, rather than a clock.

Close-up of a blue ceramic baking dish of strawberry-rhubarb crisp, with fruit filling spilling over the side

Let the finished crisp cool at least 30 minutes before serving, as it will be soupy and dangerously hot at first. As it cools to a safer temperature, the crisp will thicken up nicely, reaching what I consider its ideal consistency at about 80°F (27°C), at which point it will be saucy and warm.

If you like, serve with scoops of vanilla ice cream or a dollop of your favorite whipped cream—there's a master post of all my whipped cream recipes if you need some ideas.

April 25, 2017

Recipe Facts

Active: 20 mins
Total: 2 hrs
Serves: 12 servings

Rate & Comment

Ingredients

For the Topping:

  • 5 ounces light brown sugar (about 2/3 cup, packed; 140g)

  • 3 3/4 ounces whole wheat flour (about 3/4 cup, spooned; 105g)

  • 4 ounces old-fashioned rolled oats (about 1 1/3 cups; 115g)

  • 1 1/2 teaspoons ground cinnamon

  • 1 teaspoon whole anise seeds (optional)

  • 1 teaspoon Chinese five-spice powder

  • 1/4 teaspoon (1g) Diamond Crystal kosher salt; for table salt, use half as much by volume or use the same weight

  • 5 ounces unsalted butter (10 tablespoons; 140g), soft but cool, about 68°F (20°C)

  • 5 ounces raw pecan pieces (about 1 cup; 140g)

For the Filling:

  • 2 3/4 pounds rhubarb, cut into 3/4-inch pieces (about 11 cups; 1.25kg), from around eighteen 24-inch stalks (3 pounds; 1.35kg)

  • 10 1/2 ounces sugar (about 1 1/2 cups; 300g)

  • 2 1/2 ounces tapioca flour (about 2/3 cup; 75g), such as Bob’s Red Mill

  • 2 ounces elderflower liqueur or water (1/4 cup; 55g)

  • 3/4 teaspoon (3g) Diamond Crystal kosher salt; for table salt, use half as much by volume or use the same weight

  • 1/4 teaspoon baking soda

To Serve (optional):

Directions

  1. For the Topping: Combine brown sugar, whole wheat flour, rolled oats, cinnamon, anise seed (if using), five-spice powder, salt, and butter in the bowl of a stand mixer fitted with a paddle attachment. Mix on low speed to form a thick dough, about 5 minutes. Alternatively, this can be done by hand. Toss in pecans, transfer to a zip-top bag, and refrigerate until needed, up to 1 month.

    Collage of making streusel topping for rhubarb crisp: oats, sugar, flour, and spices in mixing bowl; hand with a clump of streusel; streusel in plastic bag
  2. For the Filling: Adjust oven rack to lower-middle position and preheat to 400°F (200°C). In the same bowl from the stand mixer (no need to wash), combine half the prepared rhubarb (about 5 1/2 cups; 22 ounces; 620g), sugar, tapioca flour, elderflower liqueur or water, and salt with a flexible spatula; the mixture will be extremely dry. Transfer to a 7- by 11-inch baking dish or 9-inch deep-dish pie pan, sprinkling any remaining sugar/starch on top, and cover with foil. Place on a foil- or parchment-lined half-sheet pan and bake until rhubarb is wilted and juicy, about 30 minutes. Meanwhile, transfer remaining fruit to the same bowl.

  3. To Finish: Remove baking dish from oven, discard foil, and sprinkle with baking soda. Stir carefully with a heat-resistant spatula until juices begin to fizz. Pour over remaining rhubarb and fold to combine, then return to baking dish. Top with handfuls of prepared streusel, flattening each addition into a thin sheet to achieve even coverage. Continue baking until crisp is bubbling in the very center, about 35 minutes more. (The time will vary dramatically depending on the exact dimensions and material of your baking dish.)

  4. Cool at least 30 minutes before serving, as the filling will be dangerously hot and extremely runny at first. The crisp will thicken as it cools to room temperature. If you like, serve à la mode or with dollops of strawberry or brown sugar whipped cream. Wrapped in foil, the crisp will keep 3 days at room temperature.

Special Equipment

7- by 11-inch glass, ceramic, or stoneware baking dish or 9-inch deep-dish pie pan; stand mixer with paddle attachment; digital thermometer; half-sheet pan

Notes

Due to disparate sourcing practices, tapioca starch manufactured outside the US may be derived from sago, which has different gelling properties from true tapioca (cassava). Look for brands that mention cassava by name; my favorite is Bob's Red Mill, available in the baking aisle of most supermarkets or online.

Make-Ahead and Storage

Wrapped in foil, the crisp will keep 3 days at room temperature.

Nutrition Facts (per serving)
437 Calories
19g Fat
64g Carbs
5g Protein
Show Full Nutrition Label Hide Full Nutrition Label
×
Nutrition Facts
Servings: 12
Amount per serving
Calories 437
% Daily Value*
Total Fat 19g 25%
Saturated Fat 7g 35%
Cholesterol 25mg 8%
Sodium 166mg 7%
Total Carbohydrate 64g 23%
Dietary Fiber 5g 19%
Total Sugars 40g
Protein 5g
Vitamin C 8mg 42%
Calcium 125mg 10%
Iron 2mg 8%
Potassium 439mg 9%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)