Heat 1 litre of water in a large pan over a high heat. Once boiling, tip in the clams. Cover with a lid and cook for 2-3 mins until the majority of the clam shells have opened. Pour into a sieve over a large jug, reserving the cooking water. Tip the reserved liquid through a muslin-lined sieve into a large non stick saucepan and set aside – this is your stock for the soup.
Discard any clams which haven’t opened, then remove three-quarters of the clams from their shells and roughly chop.
Put the bay leaf in the pan with the clam stock and tip in the potato and parsnip cubes. Cook for 5-7 mins until tender. Use a slotted spoon to remove half of the potato and parsnip and set aside. Fish out the bay leaf, spoon off any scum from the surface of the soup, then blitz the remaining stock and vegetables in a food processor until smooth, or using a stick blender.
Using the same saucepan over a medium heat, pour in the oil, add the bacon lardons, fry until crisp, then remove with a slotted spoon and set aside. Add the onion to the pan, cook for 5 mins until soft, then pour in the blitzed chowder, potato and parsnip. Heat until simmering, then tip in the chopped clams, take off the heat and stir through the crème fraîche, adding lemon juice to taste. Serve, topped with the crispy bacon, reserved clams in their shells and a scattering of chives and black pepper.