Welsh rabbit prepared in this way makes a good breakfast dish (some crisp bacon laid across the cheese wouldn't be amiss), or a good light lunch accompanied by a simple green salad.
Preheat the broiler or grill, then put the bread on a baking sheet and toast it on one side only until it's just beginning to brown. Set it aside, leaving the broiler or grill on.
Heat the ale in a sauce pan over medium heat. Melt the butter into it, then turn the heat to low and stir in the cheese. Continue stirring until the cheese is completely melted, then stir in the mustard and cayenne and the Worcestershire sauce or anchovy paste. Season the cheese mixture with plenty of black pepper.
Turn the toasted bread untoasted side up, then spread the cheese mixture on the bread slices, dividing it evenly between them. Return the toast to the broiler or grill and cook until the top of the cheese mixture is nicely browned but not burnt.