One recipe for Welsh rarebit, or Welsh rabbit, has 3 tablespoons of unsalted butter, 1 tablespoon of all-purpose flour and 1/4 cup of whole milk. It also calls for 1/2 cup of beer, preferably an ale or porter, and 1 teaspoon of dry mustard.
Additionally, Welsh rarebit calls for 1/8 teaspoon of black pepper and 6 ounces of extra-sharp Cheddar cheese, coarsely grated. The final ingredients are the yolk of 1 large egg and a baguette sliced diagonally into 16 slices.
Spread 2 tablespoons of the softened butter on one side of the bread, then place the slices butter-side up on a baking sheet. Broil the bread 4 to 6 inches away from the heat between one and four minutes. The slices should be golden brown at the end.
Melt the rest of the butter in a 1-quart saucepan. Turn the heat to low. Add the flour, and cook the mixture for one minute while whisking constantly. Add the milk and the beer in a stream, whisking. Whisk in the cheese, the pepper and the mustard.
Bring everything to a simmer over a moderately low heat. It should be about two minutes before the mixture simmers.
Remove the sauce from the heat, and whisk in the yolk right away. Pour the cheese mixture over the toasted baguettes.