Preheat oven to 400 degrees. Spray a 12 cup muffin tin with cooking spray. Divide asparagus evenly among muffin cups.
In a large bowl, beat eggs and milk. Pour eggs into each cup, filling 1/2 - 2/3 full. Sprinkle parmesan cheese into each cup.
Bake for 12-15 minutes, until eggs are set. Cool slightly before removing from pan. Don't be alarmed if the muffins puff up a lot during baking - they will settle while cooling.