This frittata is great for brunch entertaining. It can be made up to 5 days ahead; just cover, refrigerate and reheat before serving.
Let's Cook
Pre-heat oven to 300°. Cook sausage in large 12" non- stick skillet, breaking it up with a wooden spoon into small pieces.
Cook until the meat just looses it’s pink color, do not over cook, then transfer to a plate. Add Butter to skillet and melt. Add Onion and some Salt, cook until soft. Add Shallot & Garlic, cook for a few minutes until Shallot is soft. Add Spinach and cook for a few minutes. Stir in Proscuitto bits and cooked Sausage. Mix Eggs with Parmesano, Pecorino, Nutmeg, Salt & Pepper. Add Egg mixture to skillet. Mix with a large spatula and fold in the Mozzarella. Place Asparagus pieces in now, if using. Make sure everything is distributed evenly. Cook in oven at 300° for 25 - 30 minutes. May need to turn on Broiler and place skillet under broiler for about 5 minutes, until top is golden. Let cool slightly for 5 minutes, then transfer, side up, with the big spatula, to a large platter. Cool for about 1/2 hour, before covering with plastic and placing in the refrigerator, if not serving immediately.