A favorite childhood donut made perfect at home!
Add in milk, egg, butter, and vanilla extract. Stir by hand until ingredients are fully incorporated. It will be sticky. Cover with a damp towel and refrigerate for 1 hour.
While donuts are warm, submerge into the glaze one side of the donuts into the glaze. Lift and let drain into the bowl, then move the donut to a baking sheet with a cooling rack in it. (You can also place on parchment or wax paper but the glaze might pool.)