Step 1

Add the butter, cream cheese, cream and chicken stock to a saucepan. Cook over a medium heat until the butter melts - about 2 minutes. Do not boil.

Step 2

Put the egg yolk in a separate cup. Add a little of the warmed sauce to it, mixing well with a fork (this step is essential to stop the béchamel splitting).

Step 3

Add the yolk mix into the saucepan. Stir constantly over a low heat using a hand balloon whisk for about 4 minutes or until the sauce has thickened. Don't overheat the sauce or the egg yolk will curdle.

Step 4

Season with salt and nutmeg to taste.