Special equipment: a 3- to 4-inch round cookie cutter or ring mold
Preheat the oven to 400 degrees F.
In a medium bowl, beat the eggs until fluffy. Add the asparagus, Parmesan, salt and pepper.
Melt the butter in an ovenproof nonstick frying pan over low heat; add the egg mixture and cook, stirring occasionally, for about 2 minutes. Transfer to the oven until cooked through, 5 to 8 minutes.
Using a 3- to 4-inch round cookie cutter, punch out rounds from the frittata. Place each round on a toasted English muffin and enjoy!