These birthday cake donuts are delicious, simple to make, and require only basic baking ingredients. With rainbow sprinkles and vanilla, these donuts will remind you of traditional birthday cake! **The following recipe is written for high-altitude. Please follow the sea-level instructions if you live at sea-level.**
Preheat oven to 375°F (350°F for sea-level). Grease the cavities of a donut pan, and set aside.
In a medium bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. In a smaller bowl, whisk together the buttermilk, canola oil, artificial vanilla extract, and egg whites. Add the wet ingredients to the dry ingredients, and stir until just barely mixed (a few dry spots are ok). The donut batter will be the same texture as a thick pancake batter.
Using a rubber spatula, gently fold the rainbow sprinkles into the batter until there are no dry spots (don’t overmix)! Spoon the batter into a large piping bag (or a plastic bag with the tip cut off).
Pipe the batter into the donut pan cavities about 1/2 way full (don’t go more than halfway, or the batter will rise too much and you won’t get a hole in the center). Bake for about 9-10 minutes, until a toothpick comes out clean.
Let the donuts cool in the pan for about 5 minutes, and then let them cool completely on a rack. Dip each cooled donut halfway into the glaze, letting the excess glaze drip off. Decorate as desired, and let the glaze set completely, about 20 minutes. Serve! Store extras in an air-tight container for up to three days.
While the donuts are baking, whisk together the powdered sugar, milk, salt, and artificial vanilla extract in a small bowl until smooth! If the glaze is too thick, add milk 1 Tablespoon at a time until it reaches your desired consistency.
*Note: The glaze should be very thick so that it doesn’t drip too much off of the donuts – it will drip a little but shouldn’t run off. To test this, dip a spoon into the glaze. If it thickly coats the spoon, it’s good to go! If the glaze gets too thin, add more powdered sugar until it’s thick. Taste the glaze, and add more spices as desired.