
If using fresh clams and snails, steam them separately in covered pots with about 1 inch of water until cooked through; the clams should open, about 8 to 10 minutes. Strain and reserve the clam cooking liquid, then remove the clam meat from most of the shells. Set aside a few clams in the shell for serving.



Heat a medium soup pot over medium heat with a small drizzle of olive oil. Add the sliced andouille sausage and cook until browned, 4 to 5 minutes. Transfer the sausage to a plate, leaving the rendered fat in the pot.



Add the butter, fennel, onion, garlic, and minced lemongrass to the pot. Cook for about 3 minutes, stirring often, until the vegetables soften and become fragrant. Stir in the flour, Cajun seasoning, smoked paprika, and chipotle, and cook for 1 to 2 minutes to form a lightly toasted roux.



Gradually pour in the reserved clam liquid, stirring well to prevent lumps. Add enough water or bottled clam juice to bring the soup to a hearty chowder consistency, then add the potatoes. Bring to a boil, reduce to a simmer, and cook for 15 minutes or until the potatoes are tender.

Return the browned sausage to the pot, then stir in the cooked clams, snails, and heavy cream. Simmer gently for 5 minutes, stirring occasionally. Season with salt and black pepper to taste. If you want a thicker chowder, stir in a small cornstarch slurry and cook for another minute.
Ladle the chowder into bowls and top with fennel fronds if desired. Serve hot with toasted bread and a light drizzle of olive oil.