Boil the potato cubes for 15 minutes and then mash with some butter and set aside.
Fry the bacon cubes in a pan for 5 minutes and then set aside.
Add the butter to the pan and fry the onions for 5 minutes until translucent, then add the celery and garlic and cook for another 5 minutes before adding the leeks and frying for a further 5 minutes.
Add the stock to the pan along with the mashed potato and simmer for 5 minutes, then remove from the heat and coarsely blend.
Stir the cream, mustard and bacon into the blended soup and then serve.