Your topping is your choice; crushed potato chips, 1 1/2 cups coarse fresh bread crumbs mixed with 4 ounces of grated Cheddar or French fried onions from a can.
Tuna Noodle Casserole
1 small onion, finely chopped
6 ounces egg noodles (I prefer the thicker Amish style; about 3 1/4 cups)
Topping of your choice
Preheat oven to 375 degrees. Butter a shallow 2-quart baking dish.
Cook onion and pepper in 1 1/2 tablespoons butter with a pinch of salt in a 12-inch heavy skillet over moderately low heat, covered, stirring occasionally, until softened, about 5 minutes. Increase heat to moderately high and add mushrooms and thyme, then saute, stirring occasionally, until mushrooms begin to give off liquid, about 2 minutes. Add soy sauce and continue to saute mushrooms, stirring, until liquid mushrooms give off is evaporated. Add sherry and boil, stirring occasionally, until evaporated. Remove from heat.
Melt remaining 3 tablespoons butter in a 2-3 quart heavy saucepan over moderately low heat and whisk in flour, then cook roux, whisking, 3 minutes. Add broth in a stream, whisking, and bring to a boil, whisking. Whisk in milk and simmer sauce, whisking occasionally, 5 minutes. Stir in mushroom mixture, lemon juice, and salt. Flake tuna into sauce, add defrosted peas and stir gently. Check for seasoning.
Cook noodles in a 5-6 quart pot of boiling salted water until al dente. Drain noodles in a colander and return to pot. Add sauce and stir gently to combine. Transfer mixture to baking dish, spreading evenly.
Top with your topping of choice. Bake until topping is crisp and sauce is bubbling, 20-30 minutes.