Heat oven to 350degrees Fahrenheit.
Put cheeses in a mixing bowl and set aside.
In a skillet over medium high heat melt butter and saute the mushrooms until cooked, 2 to 3 minutes. Add minced garlic and chopped spinach and cook until spinach is wilted and garlic is fragrant, about 2 minutes.
Season with salt and pepper. Remove from heat. Pour over cheese, toss to mix.
Place cheese mixture into lightly buttered, oven-safe baking dish, low bowl or casuela. Sprinkle with salt and pepper.
Place in heated oven and bake until bubbling and lightly browned on top, 10-12 minutes. Dig in.