combine the butter and flour in small bowl. let cool.
Bring milk to the boil then combine with butter flour mixture.
Bring that mixture to the boil, then add the Cheddar cheese and remove from heat.
In another small pot add the ale, mustard and Worcestershire sauce. Stir on medium heat for about 5 mins. Add the ale mixture to the cheese mixture. Season well with salt and pepper. Beat in the egg yolks.
Spoon mixture onto pieces of toast then put in under the grill until cheese bubbles.