Bake for about 8 minutes, and check to see if the donuts are firm. If not, check every minute and remove from oven as soon as the donuts are firm.
Let the donuts cool to room temperature, then remove from pan and place on a parchment-lined dish or tray.
Place in freezer for a few minutes as you mix the glaze ingredients.
Remove donuts from freezer. Using a fork, dip each in the glaze and place back on the parchment-lined tray.
Set in freezer for a few more minutes to let the glaze set.
Enjoy! Store in the refrigerator.
Notes
A note about substitutions: because each type of protein powder has a distinct flavor and texture when baked, I would not try substituting different types of protein powders (other than whey protein) in this recipe. See my Recipe Basics video for examples of what goes wrong when you use the wrong protein powder.