Dene's tuna mornay

My recipe is out the Womens Weekly basic cookbook, and I adjust it as
needed:

3 tablespoons butter
3 tablespoons plain flour
1 large onion finely chopped
3 or 4 rashers of shortcut bacon, chopped
3 cups milk or part milk and part cream
corn kernels (frozen or tinned)
half a cup tasty cheese OR ricotta
1 tin tuna in springwater or brine
breadcrumbs
tasty cheese extra

melt the butter, add onion and bacon, cook until onion is transparent
add flour, cook for 1-2 minutes
remove from heat, add milk, whisking constantly, return to heat and bring to
boil
remove from heat again, add cheese, corn and tuna
place in oven proof casserole dish, sprinkle with breadcrumbs and cheese,
bake until top browns

serve with rice or pasta

optionally, cook pasta whilst you're making the mornay, mix it all together
in big casserole dish, sprinkle with cheese (no breadcrumbs this time) and
bake in oven til browned. (Homemade pasta bake, very yummy!!)