Firstly, make the cheese sauce. Melt the butter in a saucepan, sprinkle in the flour and stir until the mixture becomes a paste and continue to cook for 2 minutes.

Gradually add the milk a little at a time and whisk continuously until all the milk is added and the sauce has thickened. Add the grated cheese, mustard and season with salt and pepper to taste.

Bake the chips following the instructions on the packet.

To assemble, toast the bread and butter it. Divide the chips and pile onto half the sliced bread, pour over some of the cheesy sauce and an extra sprinkle of cheese, top with the remaining toasted bread.

Serve with tomato ketchup.