1Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8-inch baking dish.
2Heat butter and olive oil in a skillet over medium-high heat; cook and stir onion in the heated butter-olive oil until onions soften, about 10 minutes. Transfer onion to a plate to cool.
3Whisk cream, eggs, salt, and black pepper in a bowl; stir in mozzarella cheese, Parmesan cheese, and onion. Pour mixture into the prepared baking dish.
4Bake in the preheated oven until eggs are set and a knife inserted in the center comes out clean, about 35 minutes.
Footnotes
Cook's Note:
You can use a pie plate or an 8x8-inch pan. Also your quiche shouldn't be brown on top but maybe a light brown around the edges!
This doesn't rise very much, so if it looks flat it's normal.
It will be hard to get out of the pan EVEN if sprayed with Pam(R)!
Tip
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.