- Cook potato until soft, in whichever manner you prefer (steam, boil, bake, microwave). When cool, peel and rice the potato. Gently scoop into a measuring cup to measure 3/4 cup cooked potato (3 oz) and set aside.
make dough + first rise
- Sprinkle yeast over warmed milk with a pinch of sugar, stir and let sit until foamy, about 5 minutes. Whisk in butter, egg and prepared potato.
- Combine flour, sugar, salt, nutmeg and baking soda in the bowl of a food processor fitted with a metal blade, and pulse until well combined. Add liquid ingredients and mix until the dough is smooth, about one minute. Alternatively, knead by hand or with a stand mixer fitted with a dough hook (on low) for 10-15 minutes.
- Transfer dough to a lightly greased bowl and let rise in a draft-free area until puffy, but not necessarily doubled in size, about 75 minutes. The dough is ready when it partially springs back after touching it. If it rapidly bounces back, let it rise another 10-15 minutes.
shape dough + second rise
- Line a baking sheet with parchment paper, lightly grease, and set aside.
- Gently deflate the dough, place on a lightly floured surface and cut into 16 pieces. Take one piece, round into a ball and gently flatten it. Using your index finger and thumb, pierce through the center of the dough, then gently stretch into a 3" ring. Place on prepared baking sheet and repeat shaping process with remaining pieces of dough.
- Cover loosely with plastic wrap, or a clean dishcloth, and let rise in a draft-free area for about 75 minutes, or until doubled in size. At this point, the shaped doughnuts can be refrigerated overnight, then brought to room temperature before frying.
- Fill a large, heavy-bottomed pot 2 inches deep with coconut oil (warmed in the microwave, if needed, to liquefy). Attach a thermometer to the pot and heat oil over medium-high heat to 360°F.
- As the oil heats up, line a baking sheet with two layers of paper towels and set aside. Mix the sugar, ground cinnamon and grated cinnamon in a shallow bowl or large plate and set aside.
- When the oil reaches 360°F, carefully slip a few doughnuts into the hot oil, making sure not to crowd the pan. Fry for about 2 minutes, flipping once, until the doughnuts are a deep golden brown. Using tongs or a slotted spoon, carefully remove doughnuts and briefly drain on paper towel-lined pan. Dredge in cinnamon sugar mixture, place on a rack to cool, and repeat with remaining doughnuts. Make sure to wait for oil to reheat to 360°F before frying each new batch. Eat immediately!