Tuna and Corn Bake

2 tablespoons butter
1 medium onion, finely chopped
4 tablespoons flour
200mls milk
1 425g can tuna
1 can cream-style corn
2 tablespoons chopped parsley
1/4 cup dry sherry
2 sliced bread, cubed
1/2 cup grated cheese

Melt the butter and saute the onion until tender. Add the flour and cook for a minute then add the milk, stirring well. Heat until the mixture has thickened then stir in the tuna, corn, parsley and sherry and heat through. Tip into a casserole dish, top with the bread cubes and grated cheese and cook in a preheated 180C oven until the mixture is hot and bubbly and the cheese golden brown. Serve with a salad.