Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish with 1 teaspoon butter.
Whisk eggs in a large bowl. Add cottage cheese, Monterey Jack cheese, 1/2 cup melted butter, flour, spinach, mushrooms, baking powder, and salt; mix. Pour egg mixture into prepared baking dish.
Bake in the preheated oven until eggs are set and a knife inserted into the center comes out clean, about 35 minutes.
