Fresh Parsely, chopped (plus some whole sprigs for garnish)
Add milk and cream to a bowl and allow to sit at room temperature while you prepare the remaining ingredients.
Finely dice the sweet onion and celery and add to a separate bowl. Mince and add the garlic as well.
Zest the lemon and set aside.
Coarsely chop the parsley and set aside.
Pick through the crab and remove any shell pieces. Reserve 3 ounces of the crab for serving (1-1/2 ounces per person).
Melt the butter in a cast iron pot. Add the onion, celery, and garlic. salt, ground white pepper, and nutmeg. Cook until the onions and celery are softened, but not browned. 5-10 minutes.
Add the all-purpose flour to the cat iron pot, stirring to coat the onions and celery. Cook gently, making sure not to brown the flour too much. Deglaze the pot with half of the clam juice or chicken stock. Cook until the liquid mostly evaporates. 2-3 minutes.
Add the milk, whipping cream, remaining clam juice or chicken stock, and the lump crab meat to the pot. Make sure to stir very lightly so as not to entirely break up the crab meat. Bring to a light simmer and cook, whisking often. About 10 minutes.
Remove pot from the heat, add lemon zest, chopped parsley, and dry sherry. Stir to combine. Taste and season with additional salt or white peppers as needed.
Add 1-1/2 ounces of crab meat to the bottom of each of the serving bowls. Ladle the warm soup on top. Float a teaspoon or two of the dry sherry on top of the soup and garnish with remaining whole sprigs of parsley.
Serve with toasted crusty bread or oyster crackers.
Leftovers can be stored in the fridge for up to two days.