Preheat oven to 375 degrees. Bake pie crust about 10 minutes or until bottom is slightly brown. Let cool. Cook broccoli until tender; drain well. Combine milk, eggs, margarine, flour, salt, pepper and 3/4 cup cheese; whisk until well blended. Sprinkle remaining 1/4 cup of cheese over crust. Layer broccoli and mushrooms on cheese. Pour milk and egg mixture over all. Bake at 375° for 35 to 45 minutes or until a knife inserted in center comes out clean.