Make a roux with the butter and flour, and leave to cool. Bring the milk to the boil, then whisk it into the roux. Bring to the boil once again, whisking to ensure that it does not burn and also that the sauce is free of lumps. Add the cheese, beat in and remove from the heat.
Reduce the ale, English mustard and Worcestershire sauce. When thick, add this mixture to the cheese sauce. Season well with salt and pepper and beat in the egg yolks.
Spoon on to the slices of toast and grill until bubbling. Serve with extra Worcestershire sauce handed separately.
© 1988 Keith Floyd estate. All rights reserved.