Prepare a double boiler by filling the bottom with water and bringing it to a simmer.

In the top of the double boiler, combine dry mustard, paprika, cayenne pepper, and ground nutmeg.

Gradually add beer, stirring with a fork or whisk until a smooth paste forms.

Continue adding and stirring until all ingredients are well blended.

Add butter to the mixture.

Place the pan over the simmering water and cook, stirring continuously until the butter melts and the mixture is hot.

Add the grated cheddar cheese and stir with a wooden spoon until the cheese is completely melted and smooth.

Incorporate the lightly beaten eggs into the cheese mixture, stirring constantly.

Ensure the mixture does not boil while stirring. Cook until thickened and smooth.

Serve the rarebit immediately over toasted bread slices or pour it into a fondue pot or chafing dish.

Serve with toasted chunks of bread for dipping.

Garnish with fresh parsley, if desired.