1) In a saucepan set over medium heat, melt the butter, then stir in 3 tablespoons of the flour, the dry mustard, Worcestershire, salt, and cayenne until well combined.
2) Gradually stir in the beer or ale, whisking until no lumps remain and the sauce is thick.
3) Put the remaining 3 to 5 tablespoons flour in a bowl or measuring cup. Whisk in the milk, stirring vigorously to avoid lumps. Pour the milk mixture into the saucepan, whisking constantly until all the milk is added and the mixture is smooth. Cook until very hot, but not simmering.
4) Gradually add the cheese, again stirring constantly until the cheese is melted. Reduce the heat to low, and stir the sauce occasionally as you prepare the toast.
5) Slice bread 3/4" to 1" thick and toast until it's golden brown on the outside, yet still a bit soft inside. A large capacity toaster oven or 4-slice toaster is a good choice here.
6) Butter the toast, if desired. Place each piece on a plate, and pour on the cheese sauce. Serve hot.
Yield: 6 servings.