Prepare the clams: Scrub the fresh clams thoroughly under cold running water to remove any sand or grit. Discard any clams that are open and do not close when tapped. Set aside.

Cook the bacon: In a large, heavy-bottomed pot or Dutch oven, cook the 200g (7 oz) of bacon over medium heat until crispy. This will take approximately 8-10 minutes. Use a slotted spoon to remove the bacon from the pot and set it aside on a plate lined with paper towels. Leave about 2 tablespoons (30ml) of the rendered bacon fat in the pot. Discard the remaining fat, or save it for another use.

Sauté the aromatics: Add the finely chopped 1 large yellow onion (approx. 200g / 7 oz) and 2 stalks of celery (approx. 100g / 3.5 oz) to the pot with the bacon fat. Cook over medium heat, stirring occasionally, until the vegetables are softened and translucent, about 6-8 minutes. Do not allow them to brown.

Make the roux: Sprinkle the 60g (1/2 cup) of all-purpose flour over the softened vegetables. Stir continuously for 1-2 minutes to cook the flour and create a roux. This step is crucial for thickening the chowder.

Add liquid and potatoes: Gradually whisk in 500ml (2 cups) of water until the mixture is smooth. Then, add the diced 500g (1 lb) of potatoes. Bring the mixture to a simmer, then reduce the heat to low, cover the pot, and cook for about 10-15 minutes, or until the potatoes are tender but not mushy. Stir occasionally to prevent sticking.

Steam the clams: While the potatoes are cooking, place the scrubbed 900g (2 lb) of fresh clams in a separate pot with about 125ml (1/2 cup) of water. Cover and steam over medium-high heat until the clams open, about 5-8 minutes. Discard any clams that do not open. Carefully remove the opened clams from their shells. Reserve the clam liquor (the liquid released from the clams) and strain it through a fine-mesh sieve lined with cheesecloth or a coffee filter to remove any grit. You should have approximately 250ml (1 cup) of strained clam liquor.

Combine ingredients: Add the shucked clam meat and the strained clam liquor to the pot with the potatoes and vegetables. Stir gently to combine.

Add dairy and simmer: Pour in 750ml (3 cups) of milk and 250ml (1 cup) of heavy cream. Add the 30g (2 tbsp) of butter. Stir everything together. Heat the chowder over low heat, stirring frequently, until it is heated through and steaming. Do NOT boil the chowder after adding the milk and cream, as this can cause it to curdle. The chowder should be thick and creamy.

Season and serve: Season the chowder with salt and freshly ground black pepper to taste. Ladle the hot chowder into bowls. Garnish with the reserved crispy bacon and chopped fresh parsley, if desired.