Crustless Caramelized Onions and Cheese

Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease an 8-inch square baking dish or pie pan.

Step 2
Heat butter and olive oil in a skillet over medium-high heat; add onion. Cook and stir until softened, about 10 minutes; transfer onion to a plate to cool.

Step 3
Whisk cream, eggs, salt, and black pepper in a bowl; stir in mozzarella cheese, Parmesan cheese, and onion. Pour mixture into the prepared baking dish.

Step 4
Bake in the preheated oven until eggs are set and a knife inserted in the center comes out clean, about 35 minutes. It should be light brown around the edges but not brown on top.