Makes 1 1/2 cups

1 cup milk
1 tablespoon butter
1 tablespoon flour
1 egg yolk
1/2 teaspoon salt
1/4 teaspoon white pepper
1/8 teaspoon grated nutmeg
1/2 cup grated Swiss cheese

Melt the butter in a saucepan. Whisk in the flour. Add the milk and whisk until sauce is thick.
Mix in egg yolk and cook over low heat for 2 minutes. Mix in cheese. Remove sauce from heat. Season with salt and pepper and nutmeg. Pour the sauce in a container and cover with buttered wax paper. Heat before serving