Welsh rarebit

Pasos

1. Preheat the oven broiler and place the rack high enough to brown quickly without drying out the bread.
2. Toast the bread on both sides until deep golden, dry on the surface, and still slightly soft in the center.
3. Melt the butter in a saucepan over medium heat, add the flour, and stir until you get a pale paste that smells like warm biscuit.
4. Gradually pour in the beer while whisking, then let it thicken until the sauce coats the back of a spoon and becomes smooth.
5. Lower the heat, add the grated cheddar, and stir until it melts into a glossy cream, without letting it boil.
6. Stir in the mustard, Worcestershire sauce, cayenne pepper, and black pepper, then taste before adjusting the salt, as the cheese is already salty.
7. Off the heat, add the egg yolk and stir vigorously until the sauce is richer, smooth, and well combined.
8. Arrange the bread slices on a baking sheet, and generously coat them with the cheese sauce right to the edges to prevent them from burning.
9. Place under the broiler until the top blisters, browns in spots, and starts to bubble; serve immediately, piping hot.