1Preheat oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish with cooking spray.
2Layer Cheddar-Monterey Jack cheese blend and mozzarella cheese in the prepared baking dish.
3Heat 2 tablespoons butter in a large skillet over medium-high heat; saute mushrooms and green onions until mushrooms are golden brown, 5 to 10 minutes. Add spinach and tomatoes; saute just until spinach wilts, 3 to 5 minutes. Spoon vegetable mixture over cheese mixture.
4Whisk eggs, half-and-half, mustard, marjoram, tarragon, and black pepper together in a bowl; pour over vegetable mixture. Dot remaining butter on the egg mixture.
5Bake in the preheated oven until a knife inserted near the center comes out clean, 35 to 45 minutes. Let stand 5 minutes before serving.
Footnotes
Cook's Notes:
Can also add cooked meat (ham, sausage, or bacon) to sauteed vegetables if desired.
Dijon mustard can be substituted for the yellow mustard, if desired.
Use cream in place of half-and-half for fluffier eggs.