Step 1

Pour the milk into a pan, add the flour and butter, then slowly bring up to the boil, whisking continuously to a thick, smooth and glossy sauce.

Step 2

Reduce the heat and simmer for 3–5 minutes, stirring occasionally, until the flour has cooked out. Remove from the heat and season with salt and pepper. Set aside.

Step 3

Heat the grill to high and the oven to 220C/200C Fan/Gas Place the bread on a baking tray and toast one side under the grill until golden.

Step 4

Turn the bread over and spread each slice with a thin layer of mustard, followed by a layer of white sauce. Cover the sauce with a slice of a cheese and a slice of ham.

Step 5

Stack the slices into two sandwiches, then spread a thin layer of white sauce over the top and sprinkle with grated cheddar.

Step 6

Bake in the oven for 10–15 minutes until golden and bubbling. Leave to cool for 3–5 minutes before tucking in.