Preheat the oven to 350° F. Spray donut molds with nonstick spray and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In a medium bowl, whisk together the egg, buttermilk, melted butter, and vanilla. Pour this mixture into the dry ingredients, and mix until just combined. Fold in the sprinkles
Scoop this mixture into a piping/ziploc bag to pipe into the donut pan. You could also just spoon the batter into the pan if you prefer.
Fill the donut pan ½ full with batter. Don't overfill the donuts because they rise while baking. If you are using silicone donut molds, place them on a baking sheet before putting them into the oven.
Bake for 9-12 minutes until golden brown on top. Transfer the donut pan to a wire rack and allow the donuts to cool for about 5 minutes. Carefully take the donuts out of the pan and allow them to cool before icing.
Chocolate Icing
In a large bowl, whisk together the powdered sugar, cocoa powder, 1.5 tablespoon milk, and vanilla until smooth. Add up to 1 tablespoon more milk until you reach the desired consistencyDip the cooled donuts right into the chocolate glaze and top with sprinkles immediately. If you want the icing to set, allow them to sit for 30 minutes to an hour before serving.
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Notes
Don't overfill the donut pan- Overfilling the donut pan can cause your donuts to rise and spill out over the tops- trust me, I've done it a million times. Try to fill your donut mold ½ way or just a little more.
Every oven is different- be sure to watch your donuts carefully in order to not overbake or undertake them. The pan you use to make your donuts will also change the amount of time needed.
Not a fan of chocolate icing?- Make vanilla icing for your sprinkle donuts by mixing together 1 cup powdered sugar, 1-2 tablespoon milk, and ¼ teaspoon vanilla extract.