Spinach-Filled Mushrooms
["16 to 20 mushrooms (1 1/2 to 2 inches)", "1 c. finely chopped onion", "3 Tbsp. butter or margarine", "1 (10 oz.) pkg. chopped frozen spinach, cooked according to pkg. directions and drained", "1/2 c. grated Swiss cheese", "grated Parmesan cheese"]
["Remove stems from mushrooms.", "Chop stems finely and saute with onion in butter until tender, but not brown.", "Add spinach.", "Stir to mix thoroughly.", "Add Swiss cheese, stirring lightly.", "Remove from heat."]
["mushrooms", "onion", "butter", "frozen spinach", "Swiss cheese", "Parmesan cheese"]