"Brings back childhood memories of staying home with Mum and making these delicious cheese on toasts. The cheese sauce is also wonderful for topping fish or roasted veggies. Do use a heavy British or European beer."
Melt butter in a saucepan oven low heat. Add flour and whisk for 2 to 3 minutes, being careful not to brown the flour. Whisk in Worcestershire sauce, mustard, salt, and pepper until very smooth. Whisk in beer. Pour in heavy cream and whisk until smooth. Add Cheddar cheese gradually, stirring constantly, until melted and smooth, about 5 minutes.
Remove cheese sauce from the heat and let cool, about 5 minutes. Whisk in egg yolks.
Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Toast bread slices on 1 side. Arrange on a baking sheet with the untoasted side facing up. Spoon cheese sauce over the untoasted side.
Place under the preheated broil until bubbling and golden, 2 to 3 minutes.