Step 1

Heat oil and butter in a large heavy pot over medium. Add potatoes, leeks, celery, and thyme sprigs; season with salt and pepper. Cook, stirring occasionally, until leeks are tender, about 5 minutes. Add wine, bring to a boil, and cook until reduced by half, about 2 minutes. Add stock and cream, season with salt and pepper, and bring to a gentle simmer (if using clam juice, taste before adding salt, it's very briny). Cook until potatoes are starting to fall apart (their starch will help give body to the soup), 50-60 minutes.

Step 2

Add clams to pot and stir to coat. Cover and simmer until clams are just beginning to open, 10-12 minutes. Season cod with salt and pepper and add to pot. Reduce heat to low and cover. Let fish gently poach until cooked through, about 5 minutes (simmering too hard can make fish tough). Season with salt and pepper, if needed, and serve topped with thyme leaves, with hot sauce and lemon wedges.