Preheat oven to 170° fan

Grease an ovenproof dish

Cool pasta according to instructions on the packet

Melt the butter in a saucepan

Fry the onion and bacon

Stir in the flour and cook for 1 minute

Remove from heat and gradually and the milk

Whisk until you have a smooth sauce

Bring to the boil and simmer for a few minutes

And most to the cheese and salt and pepper to the pot

Add the pasta and stir until it is fully coated

Pour into the ovenproof dish

Sprinkle with the remainder of the cheese and the breadcrumbs

Cook for 15-30 minutes, until the top is golden brown

Serve