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.
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).
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.
Season with salt and nutmeg to taste.
1.9g net carbs per portion. Makes 4 generous portions of ¼ cup (4 tablespoons or 60g each).Change up the flavour by adding one or more of the following ingredients:
shredded mozzarella or cheddar for a Keto Cheese Sauce
grated parmesan, gruyere or Emmental (to make a low carb sauce mornay)
white wine or sherry
puréed sautéed onions
Take care not to overheat the sauce or it can split.Easy hack if it does split or become lumpy: Take it off the heat immediately and pulse with an immersion blender. Store in the fridge for up to 4 days or freeze for up 1 month.