Spinach Bars
["4 Tbsp. butter", "3 eggs", "1 c. flour", "1 c. milk", "1 tsp. salt", "1 tsp. baking powder", "1 lb. grated Cheddar cheese", "1 small chopped onion", "1 (10 oz.) pkg. frozen chopped spinach, thawed and drained", "1/2 c. mushrooms, chopped (optional)"]
["In a 9 x 13-inch pan, melt the butter.", "Mix remaining ingredients together and spoon into pan.", "Bake at 350\u00b0 for 35 minutes.", "Cool slightly before cutting into squares.", "Can be served hot or at room temperature."]
["butter", "eggs", "flour", "milk", "salt", "baking powder", "Cheddar cheese", "onion", "mushrooms"]