Preheat the oven to 350 degrees Fahrenheit. Spray two 6 cavity donut pans with oil (we'll be making 8-9 total, depending on your pan). Set aside. If you only have one pan, don't worry, just do two batches! Whisk together all wet ingredients. When measuring the champagne, be sure to let the bubbles dissipate before adding to the bowl to ensure you have a full 1/4 cup + 2 tbsp of champagne and not that amount of just bubbles.
Whisk in the dry ingredients, making sure to spoon and level the flour.
Fill each donut cavity with about 1/4 cup of batter. You want a little bit of space between the top of the batter and the top of the pan.
Bake for 10-14 minutes or until a toothpick comes out clean. Let cool for 10 minutes, then flip the pan over onto a cooling rack to finish cooling. They should slide right out, but if they don't just gently tap the bottom of the pan until the come out.
To make the glaze, whisk together the sugar, vanilla, champagne and milk as needed to thin. I like it on the thicker side, if it's too thin it kind of just absorbs right into the donuts and looks translucent. If you want a nice white glaze like the photos, keep it on the thicker side.
Dunk the top of each donut into the glaze once cool (after about 30 minutes they're good to go), then immediately top with sprinkles. Enjoy!