Render the pork fat: In a large heavy-bottomed pot, cook the diced salt pork over medium heat, stirring occasionally, until the fat is rendered and the meat is crispy, about 5–7 minutes. Remove the crisped bits with a slotted spoon and set aside.
Soften the onion: In the same pot with the rendered pork fat, add the diced onions and cook until soft and translucent, about 3–4 minutes, stirring occasionally.
Make the roux: Sprinkle the flour over the onions and stir constantly for 1–2 minutes to cook out the raw flour taste. Do not brown.
Build the base: Slowly whisk in the clam juice, stirring to break up any lumps. Add the bay leaves and bring to a gentle simmer.
Cook the potatoes: Add the diced potatoes and simmer until just tender, about 12–15 minutes. The potatoes should hold their shape but be fork-tender.
Temper the dairy: Remove the pot from heat. In a separate bowl, gently warm the milk and heavy cream together (do not boil). Slowly stir the warm dairy into the soup, stirring constantly to prevent curdling.
Add the clams: Stir in the chopped clams along with their juice. Add the reserved pork crisps back in.
Final seasoning & gentle heat: Return the pot to low heat (do not boil). Season with salt and pepper. Heat gently until steaming, about 2–3 minutes. Remove the bay leaves before serving.
