Step 1

Melt the butter in a heavy bottomed saucepan over low heat. Add the flour and whisk until smooth. Cook, stirring, for about half a minute until the flour is light golden brown.

Step 2

Add the beer and cream, stirring constantly. Stir in the cheese, a bit at a time, whisking it in to melt. Make sure the mixture does NOT boil. Cook until all the cheese has melted and the mixture is smooth. Remove from the heat.

Step 3

Beat the egg together with the mustard powder and cayenne. Temper with a bit of the hot mixture and then whisk the whole lot back into the melted cheese mixture.

Step 4

Return to the heat and cook for a further 2 to 3 minutes, or until the mixture has thickened. Pour the mixture over the hot toast and serve immediately.

Step 5

Alternately you can spread the mixture over the toast and pop under a hot grill until it is bubbling and golden brown.