Warm whole milk to 100-110°F, stir in active dry yeast and 1 teaspoon sugar, then let sit 10 minutes until foamy on top. Avoid milk temperatures colder or hotter than recommended.
2 teaspoons active dry yeast, 1 ¼ cups whole milk, 2 teaspoons granulated sugar
Combine flour, remaining sugar, and salt in a large bowl. Add proofed yeast mixture, eggs, softened butter, and vanilla extract. Knead by hand or with a stand mixer for 8-10 minutes until smooth, elastic, and slightly tacky.
4 cups all-purpose flour, 2 teaspoons granulated sugar, 3 eggs, ¼ cup unsalted butter, 1 teaspoon vanilla extract
Place dough in a greased bowl, cover with a damp towel, and let rise at 75°F for 60-90 minutes until doubled in size.
Punch down dough gently, roll out to ½-inch thickness on a lightly floured surface, cut into 3-inch rounds, place on parchment-lined baking sheet, cover, and let rise 30 minutes until puffy.
4 cups all-purpose flour
Heat vegetable oil in a deep pan to 350°F. Fry 3-4 doughnuts at a time for 2-3 minutes per side until deep golden brown. Drain on a cooling rack and wait 30 seconds before frying the next batch to maintain oil temperature.
for frying vegetable oil
Inject each fried doughnut with fruit preserves using a pastry bag or spoon if desired. Dust doughnuts with powdered sugar while still slightly warm.
½ cup fruit preserves, to dust powdered sugar
