Place the foil-lined baking cups on a cookie sheet; fill 1/2 to 2/3 full with batter and bake. Make sure to keep space between the liners to allow for expansion. Plus you don't have to worry about washing your pan between batches.
Don't have a muffin pan? No worries: Reynolds® StayBrite® Baking Cups are sturdy enough to use without muffin pans.