Preheat oven to 350 F and fill a standard-sized muffin tin with silicone liners. (You can also try brushing a metal muffin tin with butter, but they might not pop out as flawlessly as they do from silicone.)
In a pan over medium heat, melt the butter and add the chopped onions. Saute until soft and beginning to brown, about 5 minutes.
Meanwhile, chop the asparagus spears into bite-sized pieces.
Add the asparagus spears to the pan and saute briefly until just beginning to turn bright green.
Stir in the frozen peas and carrots until they’re just warmed through, then remove from heat and salt to taste.
In a large mixing bowl, fork-whisk eggs, cottage cheese, Mozzarella, and Parmesan.
Fold in the vegetable mixture.
Scoop the egg and veggie mixture into 12 silicone muffin cups.
Bake 15-20 minutes until egg is set. Let cool slightly before serving.