3 tablespoons (43 grams) unsalted butter, melted and cooled to lukewarm
1/2 cup buttermilk, at room temperature
2 large eggs, at room temperature
3/4 cup (150 grams) granulated white sugar
1 1/2 teaspoons pure vanilla extract
Vegetable, canola, refined coconut oil, vegetable shortening, or peanut oil, for frying
For the chocolate glaze:
1 stick (113 grams) unsalted butter
1/4 cup whole milk
1 tablespoon light corn syrup*
2 teaspoons vanilla extract
4 ounces semisweet chocolate, chopped
2 cups (250 grams) powdered sugar, sifted
Rainbow sprinkles, if desired
For the doughnuts:
In a large bowl, mix together the flour, baking powder, salt, and nutmeg. Combine butter and buttermilk in a small bowl or measuring cup, and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the eggs and sugar until thick and pale, about 5 minutes. Beat in the vanilla extract. On low speed, alternately add the flour mixture with the melted butter and buttermilk, starting and ending with the flour. The dough will be soft. Cover tightly with plastic wrap and let sit at room temperature for 30 minutes, or until the dough is firm enough to handle.
MAKE AHEAD: At this point you can also refrigerate the covered dough for up to 48 hours. Let come to room temperature before proceeding with recipe as written.
Turn the dough out onto a floured work surface. Roll the dough out into just over 1/4-inch thickness and cut with a doughnut cutter or with a large round cutter and a small cutter for the holes. Brush off any excess flour and place the doughnut shapes on a lightly floured parchment lined baking sheet. Cover and let the doughnuts sit at room temperature while you heat the oil.
Heat at least 1 1/2 inches of oil in a large and heavy pan to 350°F. Place three to four doughnuts in the oil at a time and fry until golden brown, about 1 minute or less per side (30 seconds for the holes). Do not overcook the doughnuts. Drain on a paper towel-lined plate.
For the chocolate glaze:
In a medium saucepan over medium heat, combine the butter, milk, corn syrup, and vanilla and heat until the butter melts. Decrease the heat to low and add the chocolate, whisking until melted. Turn off the heat and add the powdered sugar, whisking until smooth.
Immediately dip the doughnuts into the glaze. If the glaze begins to set, return the saucepan to low heat and stir until liquid again. Garnish with sprinkles, if using. Let the glaze set on the doughnuts for 30 minutes before serving.
Doughnuts are best made the day they’re fried. However, you can store the glazed doughnuts in an airtight container for up to 2 days.