Welsh Rarebit

In a heavy based pan, melt the butter and add the flour. Whisk it for about 2 min. Add the English mustard, Worcestershire sauce and pour in the beer gradually, whisking well until incorporated. Add the cream and, finally, the cheese. Stir until the cheese is melted and the mixture is smooth. Remove from the heat and add the egg yolks. Season well with salted pepper. Serve it over the toasted bread.