1. Combine the meat with the chopped onion, mustard and herbs in a bowl until well mixed.
2. Season well with salt and pepper then work in sufficient beaten egg (approximately half a medium egg) to bind well.
3. Form the mixture into balls by rolling generous teaspoonfuls between your hands.
4. Heat a little oil in a large pan and gently fry the meatballs - turning frequently, until browned on the outside and cooked through – this will take a good 15 minutes and you may have to do this in two batches. Keep cooked meatballs warm while frying the second batch.
5. Cut the Castello® Extra Creamy Blue Slices into three equal pieces. Using a serrated knife, halve the meatballs through their ‘equator’, then sandwich together again with two pieces of cheese between the two halves.
6. Return to the pan to just start to melt the Castello® Extra Creamy Blue Slices and then serve with pasta of your choice.