Preheat oven to 350 degrees F. Generously grease two 6-cavity doughnut pans with cooking spray or melted butter. Set aside.

To make the doughnuts, in a large bowl whisk together the flour, sugar, baking powder, baking soda, and salt until evenly combined. Set aside. In a large measuring cup or medium bowl, whisk together the buttermilk, vanilla, egg, and melted butter until smooth. Make a well in the center of the dry ingredients and pour in the wet ingredients. Stir with a rubber spatula until just combined, making sure not to over-mix. Fold in about 2 tablespoons of sprinkles. Transfer the mixture to a pastry bag or a resealable plastic bag with the end snipped off.

Pipe out the batter among the prepared doughnut pan, until they're about 3/4 of the way filled. Bake for 10 to 12 minutes, or until the doughnuts spring back when touched, or a toothpick inserted in the middle comes out clean. Allow to cool in the pan for 5 minutes, before inverting them onto a wire rack.

To make the glaze, whisk together the sugar, butter, vanilla, and enough milk to get the perfect consistency for dipping the doughnuts. It should be thin but somewhat thick at the same time. Dip the cooled doughnuts into the glaze and then top with sprinkles. Allow the glaze to set before eating. Enjoy!