Why It Works
- Browning butter packs in tons of flavor, without dulling the sweet potatoes.
- Slow-roasting the sweet potatoes activates endogenous enzymes that bring out their natural sweetness.
- A touch of maple syrup and a bit of chopped thyme are the only embellishments these naturally sweet sweet potatoes need.
Have you ever wondered why sweet potatoes are so darn insecure? It's time to say good-bye to the days of hiding sweet potatoes behind sugar and bolted-on marshmallows. What we have here is a technique for making mashed sweet potatoes that are so sweet, rich, and packed with sweet-potato flavor, they need only the simplest of embellishments to shine.
- 4 pounds (1.8kg) moist sweet potatoes, such as ruby or garnet yams (about 4 large potatoes; see note)
- 8 sprigs thyme, divided
- 6 tablespoons butter (3 ounces; 85g)
- 1/4 cup (60ml) maple syrup
- Kosher salt
Adjust oven rack to center position. Place 2 large sheets of heavy-duty aluminum foil on a work surface. Working with 1 sheet at a time, place half of potatoes in center along with 3 sprigs of thyme. Fold up foil and crimp edges to seal tightly. Repeat with other half of potatoes. Transfer pouches to a rimmed baking sheet and place in oven. Set oven to 300°F (150°C). Roast until a thin skewer inserted into potatoes meets no resistance, about 2 hours. Remove potatoes from oven and set aside until cool enough to handle.
Meanwhile, melt butter in a medium saucepan over medium-low heat, swirling gently, until particles are pale golden brown and smell nutty. Immediately transfer to a large bowl or the bowl of a stand mixer fitted with a whisk attachment. Add maple syrup. Pick leaves off of remaining 2 thyme sprigs, roughly chop, and add to bowl.
Peel sweet potatoes and discard skins. Add flesh to bowl with butter and syrup. Beat with whisk attachment or a handheld mixer until smooth and fluffy, about 2 minutes. Season to taste with salt. Serve. See note for make-ahead suggestions.
Sweet potatoes can be made even sweeter by pretreating them in a water bath to activate their enzymes. To do this with a sous vide–style circulator, set your circulator for 150°F (66°C). Place the sweet potatoes in the water bath and let circulate for 2 to 4 hours before proceeding with the recipe. To do this with a beer cooler, fill your cooler with water at 170 to 175°F (77 to 79°C). Add the potatoes, cover, and let rest for 2 to 4 hours before proceeding.
To Make Ahead: Sweet potatoes can be refrigerated for up to 5 days. To store and reheat, transfer the sweet potatoes to a heavy-duty zipper-lock bag with the air pressed out. Reheat by completely submerging the zipper-lock bag in a pot full of hot (not boiling) water, removing the bag occasionally to squeeze contents around, until fully reheated, about 30 minutes. The best way to do this is with a sous vide–style circulator set at 150°F.