Step 1

In a small saucepan melt the butter and make a roux with the flour. Cook for a couple of minutes, stirring to prevent the roux from burning. Stir in the warm beer by degrees, until you have a thick but smooth sauce. Add the grated cheese and stir until melted. You should now have a thick paste. Mix in the mustard and Worcestershire sauce and season well with black pepper.

Step 2

Lightly toast and butter the bread, then pile up the cheesy mixture on each slice. Cook under a hot grill for a few minutes, until browned and bubbling.