Prepare the Broth: In a medium bowl, combine the oyster liquor, clam juice, and chicken stock. Set aside.
Crisp the Bacon: In a large soup pot over medium heat, cook the diced bacon until golden brown, rendering the fat. Use a slotted spoon to remove the bacon to a paper-towel-lined dish; set aside for garnish.
Sauté Aromatics: Pour off all but 1 tablespoon of the bacon fat from the pot. Add the butter and the sliced leeks. Sauté until soft and translucent (about 5–7 minutes). Stir in the bay leaf and minced garlic, sautéing for another 30 seconds until fragrant.
Simmer Potatoes: Add the reserved broth mixture and the diced potatoes to the pot. Bring to a boil, then reduce the heat and simmer until the potatoes are tender on the outside but still firm on the inside (about 10–12 minutes).
Thicken and Season: Use a spoon to smash a few of the cooked potatoes against the side of the pot to thicken the broth naturally. Stir in the nutmeg, lemon zest, lemon juice, salt, and pepper.
Finish with Cream: Pour in the heavy cream and bring the mixture back to a gentle simmer. Add the spinach and stir until just wilted.
Cook the Oysters: Add the shucked oysters and a pinch of red pepper flakes. Cook the oysters in the stew, simmering for another 3–4 minutes.
Serve: Ladle into warm bowls, garnish with the reserved crispy bacon, minced parsley, a scattering of oyster crackers, and serve immediately.