I like making frittatas on Sunday mornings so I can have quick, healthy, and easy breakfasts for a few days during the week. They are so easy to make, can use up whatever you have in the refrigerator, and they are a healthy way to start your day. I found some mushrooms, onions, spinach, and Swiss in the fridge so that’s what I used in this frittata but it would also be good with bacon, ham, or sausage in there too.
Preheat the oven to 350 degrees. Coat a tart pan with cooking spray.
Heat the olive oil in a large skillet over medium high heat. Add the onions and mushrooms then cook stirring often until caramelized, about 15-20 minutes. Add the spinach to the skillet then season with sea salt and freshly cracked pepper, to taste. Toss until well combined.
Place some of the mushroom & onion mixture and Swiss cheese into the bottom of the tart pan. Combine the eggs with the milk then season with sea salt and freshly cracked pepper, to taste. Whisk the eggs until they are mixed thoroughly.
Pour the egg mixture into the tart pan then add the remaining onion mixture and Swiss cheese to the top.