Place the butter into a large saucepan & melt over a medium heat.
Stir in the flour then cook out for 1 minute, stirring constantly.
Add in half the milk, whisk until smooth & cook out until thick, stirring regularly. This will take 2-3 minutes over a medium heat.
Next, pour in the remaining milk & keep cooking until thickened again.
Now add in half the chicken stock & reduce the heat to medium-low. Continue cooking, stirring/whisking regularly until the sauce has thickened back up.
Pour in the rest of the stock then keep cooking until the flour has been cooked out & the sauce has thickened for a final time.
Reduce the heat to low, add in the mustard, nutmeg & cheeses then stir until melted. Season the sauce with salt & pepper then take off the heat.
Give the cheese sauce a good blitz with a stick blender then leave to cool.
In the meantime, chop the turkey, stuffing & pigs in blankets into 1-2cm pieces. Once the sauce is cool, add in the leftovers & chopped parsley then stir to combine.