Step 1

Preheat the grill to a medium heat.

Step 2

Melt the butter in a saucepan and whisk in the flour and mustard powder. Cook for a minute or two, then gradually add the stout and the Worcestershire sauce, stirring constantly until smooth. Bring to the boil and immediately reduce the heat.

Step 3

Add the cheese and stir until it has melted. Remove from the heat and leave to cool a little. Add the egg yolks and mix well.

Step 4

Toast the bread, then arrange on a wire rack or baking tray. Spoon the sauce onto the toasted bread, spreading it out almost to the edges. Grill until browned and slightly puffed up. Serve immediately.