Tuna Noodle Casserole

3 tablespoons butter or margarine
2 tablespoons flour
1 tablespoon onion, minced
1 teaspoon salt
1/8 teaspoon pepper
2 cups milk
4 cups egg noodles
1 large can tuna
1 can sweet peas

Make sauce of melted margarine, flour, onion, salt and pepper, adding milk all at once. Cook over medium heat until thick and smooth.

Cook noodles. Combine all ingredients in greased casserole. Bake at 350 degrees F for 30 minutes.