Preheat oven to 350°F. Grease a donut tin with nonstick spray. Set aside.
In a large bowl, whisk the flour, sugar, and baking powder together.
1½ cups all-purpose flour, ¾ cup granulated sugar, 2 teaspoons baking powder
In another bowl, whisk the milk, vegetable oil, butter, egg, and vanilla together.
½ cup whole milk, ⅓ cup vegetable oil, 3 tablespoons unsalted butter, 1 large egg, 1 teaspoon pure vanilla extract
Pour the wet ingredients to the dry and mix just until combined.
Gently fold the sprinkles into the batter.
¼ cup rainbow sprinkles
Divide the batter between the wells of the donut pan, filling each one with about ⅓ cup of batter. For ease, transfer the batter to a Ziplock bag, cut the corner off, and pipe the batter into each donut well. (If your donut pan has 6 wells, bake the donuts in batches.)
Bake for 16-18 minutes, or until a toothpick inserted into a donut comes out clean.
Transfer the donuts to a wire rack and allow them to cool completely before glazing.