- 1 russet potato
- 1/2 cup heavy cream
- 2 teaspoons (1 envelope) active dry yeast
- 4 cups unbleached all-purpose flour, plus more for dusting
- 2 jumbo eggs
- 3 tablespoons sugar
- Pinch of salt
- 4 tablespoons unsalted butter, cubed and softened
- Zest of 1 lemon
- Juice of 1 lemon or 1 tablespoon lemon extract
- 3 teaspoons ground cinnamon, for garnish
- 1 cup vanilla sugar, for garnish
- Vegetable oil, for greasing the bowl and for frying
- Confectioners’ sugar, for garnish
1. Place the potato in a small saucepan and cover with water. Bring to a boil over medium heat and boil for 8–10 minutes. Drain the potato. When the potato is cool enough to handle, peel, then mash it in a bowl.
2. In a separate saucepan, heat the heavy cream, but do not bring it to a boil. Transfer the cream to a small bowl, add the yeast, and stir until dissolved. Allow the yeast mixture to rest for 20–25 minutes.
3. Pour the flour onto a clean wooden or marble-like surface in a mound and form a well in the center of the flour. In a separate mixing bowl, combine the mashed potato, eggs, sugar, salt, butter, and lemon zest, and whisk together. Pour the egg mixture into the well of the flour, along with the lemon juice, the heavy cream–and–yeast mixture, and 1/4 cup of warm water. Using your hands, fold the flour into the mixture until a dough is formed. Place the dough in a lightly oiled bowl, cover, and set aside for 1 hour.
4. Turn over the dough onto a lightly floured surface and knead the dough for 3–4 minutes. Cut one-quarter of the dough and cover the rest of the dough with a kitchen towel.
5. Roll the dough with your hands into a rope about 1 inch wide. Cut the rope into 6-inch pieces and form each piece into a circle, pinching the ends to secure. Place the doughnuts on a baking sheet and cover with a kitchen cloth; set aside in a warm place for 30 minutes to allow the doughnuts to rise. Combine the cinnamon and vanilla sugar in a bowl large enough to hold one doughnut.
6. Pour enough oil into a deep skillet to reach a depth of 3 inches and heat over medium heat until hot. (To see if the oil is ready for frying, add a pinch of dough to the oil; if it bubbles, it is ready.) Place 3–4 doughnuts in the oil (do not overcrowd the pan) and fry, turning once or twice with tongs for even frying, for 30–45 seconds total. Transfer fried doughnuts with tongs to a paper towel–lined wire rack and allow oil to drain briefly. Dip doughnuts while still warm in the sugar mixture and place on a separate wire rack. Garnish with confectioners’ sugar and serve warm.