- 3 tablespoons unsalted butter, softened
- 3/4 cup granulated sugar
- 1 large egg, at room temperature
- 1 1/2 teaspoons vanilla extract
- 1 cup lightly packed mashed russet or Yukon Gold potatoes (see “Additional Notes,” below)
- 1/4 cup buttermilk, at room temperature
- 2 cups all-purpose flour, plus more for work surface
- 1 teaspoon baking powder
- 1 teaspoon baking soda
- 1/2 teaspoon table salt
- 1/2 teaspoon freshly grated nutmeg
- Vegetable shortening or vegetable oil for frying (see “Additional Notes,” below)
- Cinnamon sugar, for dusting (optional)
In a large bowl, cream the butter and sugar with a standing or handheld mixer until fluffy, about 1 minute. Add the egg and vanilla and beat until glossy and pale yellow.
Add the potato and buttermilk and beat until smooth. Add the flour, baking powder, baking soda, salt, and nutmeg and beat just until evenly combined. The dough should now be fairly easy to handle, but still a bit sticky.
Generously dust your counter with flour (the recipe is calibrated so that the dough can absorb this flour without getting dry). Turn the dough out onto the counter and flip to coat with flour.
With your hands, gently press the dough out to a ½-inch thickness and cut into rounds using a doughnut cutter or two biscuit cutters (a large and a small). Gather the scraps and gently press out again as needed to use up all the dough.
Fill a Dutch oven with oil or shortening to a depth of 2½ inches. Set over medium heat and bring the temperature to 375° (check with a thermometer). Working in small batches, cook the doughnuts in the oil, turning once, until puffed and golden brown on both sides, 2 to 4 minutes per side. As you fry, you may need to reduce or increase the heat to maintain a steady temperature. Check it periodically with the thermometer.
Transfer the cooked doughnuts to paper towels to drain. If desired, toss them in cinnamon sugar when they’re cool enough to handle. Serve warm or at room temperature.
The drier your potatoes are, the lighter your doughnuts will be, so we bake or microwave them, rather than boil them. Running the cooked spuds through a potato ricer gives a fluffier texture. When it comes to frying doughnuts, we find that melted vegetable shortening produces a crisper crust. Feel free to just use leftover mashed potatoes, though, provided they aren’t flavored with garlic, chives, etc.