Scalloped Potatoes
["1/4 c. chopped onion", "1/2 tsp. salt", "1/8 tsp. pepper", "2 Tbsp. margarine", "2 Tbsp. flour", "1 1/4 c. milk", "3 medium potatoes, peeled and thinly sliced (3 c.)"]
["For Sauce:", "Cook onion in the margarine until tender.", "Stir in flour, salt and pepper.", "Add milk all at once.", "Cook and stir until thickened and bubbly.", "Remove from heat."]
["onion", "salt", "pepper", "margarine", "flour", "milk", "potatoes"]