In a large saucepan, fry a chopped onion and garlic in butter. Separately fry a few chopped rashers of streaky bacon - I do this separately because the bacon provides more than enough fat to cook itself.
Once the onion is golden and the bacon is crispy, add the bacon to the pan. Add chopped leek and diced potato and saute for a few minutes. Add stock and seasoning, bring to the boil and simmer until the veggies are tender. At this point, you can either blend for a smooth soup, or leave it chunky.
Stir in a good measure of cream and boil to thicken.
Add some more crispy bacon to finish, and serve with warm crusty bread.