½ bag egg noodles 2 cans of water-packed tuna, flaked 2 cups fresh or frozen peas For the sauce: 2 tablespoons butter 1 small white onion, finely chopped ¼ cup unbleached all-purpose flour 1 1/3 cups whole milk salt and pepper to taste For the topping: 1 cup cheddar cheese, grated 1 cup crushed potato…