Ingredients:
Dough: 1½ cups flour, ¼ cup sugar, ¼ tsp salt, 2 tsp yeast, ¾ cup warm milk, 3 Tbsp oil, 2 egg yolks, 1 tsp vanilla, extra flour as needed.
For Coating: 3 Tbsp melted butter, ½ cup sugar
Custard Filling: ¼ cup sugar, 2 Tbsp cornstarch, 1 cup milk, 1 egg yolk
Steps:
Dough: Combine warm milk, sugar, and yeast; let sit until bubbly. Add oil, yolks, vanilla, flour, and salt; mix until smooth. Knead on floured surface for 5 mins. Cover and let rest 10-15 mins.
Custard Filling: In a saucepan, combine sugar and cornstarch, add milk and yolk. Boil for 1½ mins while stirring, then chill.
Shape & Bake: Roll dough ½-inch thick, cut circles, place on greased sheet, and let rise 1 hour. Bake at 350°F for 10-12 mins.
Coat & Fill: Brush warm donuts with melted butter, roll in sugar, then fill with custard or jam.