Scalloped Tuna
["4 c. thinly sliced potatoes", "3 Tbsp. butter", "1/4 c. flour", "2 Tbsp. prepared mustard", "1 tsp. salt", "1/8 tsp. pepper", "2 c. milk", "1 (7 oz.) can solid tuna", "1 c. thinly sliced onion"]
["Boil potatoes in salted water for 10 minutes.", "Melt butter; blend in flour, seasonings and milk, gradually.", "Bring to a boil."]
["potatoes", "butter", "flour", "mustard", "salt", "pepper", "milk", "tuna", "onion"]