Why It Works
- Blending butter and flour minimizes gluten development, for an ultra-tender muffin-like cake.
- A small portion of fragrant, lemony coriander makes the blueberry flavor seem more intense.
- Lemon juice and salt balance the sweetness of the saucy blueberry layer.
Classic blueberry muffins are perfect for breakfast on the go, but for a lazy breakfast or brunch, this upside down format presents the opportunity to grab a plate and slow down. It's served warm, with a thick layer of jammy fruit over a light and tender muffin base that's scented with a pinch of lemon zest. Even better, the dry "mix" can be held overnight at cool room temperature, then pulled together in about 5 minutes when you're ready to bake.
- For the Batter:
- 12 ounces all-purpose flour, such as Gold Medal (2 1/3 cup, spooned; 340g)
- 5 1/4 ounces plain or toasted sugar (3/4 cup; 145g)
- 2 teaspoons baking powder
- 2 teaspoons lemon zest, from 1 small lemon
- 1 teaspoon (4g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
- 1/4 teaspoon baking soda
- 1/4 teaspoon ground coriander seed
- 1/8 teaspoon grated nutmeg
- 6 ounces unsalted butter (1 1/2 sticks; 170g), cut into 1/2-inch cubes
- 5 ounces milk, any percentage will do (about 1/2 cup plus 2 tablespoons; 140g)
- 2 large eggs, straight from the fridge (about 3 1/2 ounce; 100g)
- 2 teaspoons (10g) vanilla extract
- For the Topping:
- 16 ounces fresh blueberries, rinsed and dried (2 2/3 cups; 455g), see note for using frozen fruit
- 1 3/4 ounces sugar (1/4 cup; 50g)
- 1 1/2 ounces lemon juice, from 1 small lemon (about 3 tablespoons; about 45g)
- Salt, to taste
Adjust oven rack to middle position and preheat to 350°F (180°C). Line a 10-inch cast iron skillet with parchment paper and set aside. Combine flour, sugar, baking powder, lemon zest, salt, baking soda, coriander, nutmeg, and butter in the bowl of a stand mixer fitted with a paddle attachment. Mix at low speed to form a mealy powder, about 2 minutes. If you like, this "mix" can be held overnight at cool room temperature in an airtight container. To proceed, transfer to a large bowl and stir in the milk, eggs, and vanilla (if using).
Transfer blueberries to the parchment-lined skillet and shake gently to distribute in an even layer. Sprinkle with sugar, lemon juice, and salt. Dollop batter over the surface as evenly as possible, then smooth with an offset spatula. Bake until muffin is puffed and golden brown, about 45 minutes. The exact bake-time will vary depending on the skillet's gauge, so keep a close eye on it to prevent overbaking.
To serve, run a dull knife around the edge of the pan to loosen the muffin, invert a large plate or platter over the top, and flip. Wait about 30 seconds, then remove the cast iron skillet, taking care to avoid the cloud of steam it will release. Cut generous wedges and serve immediately, as leftovers will stale rapidly overnight.
For frozen blueberries, measure while frozen if using cups, as thawed fruit will wilt and compress. Thaw to at least 40°F (5°C) before use, or the frozen fruit will chill the bottommost layer of muffin batter and cause it to bake at a different rate.