Heat a large stockpot or Dutch oven over medium high heat. Add bacon and cook until brown and crispy, about 6-8 minutes. Transfer to a paper towel-lined plate, reserving 1 tablespoon excess fat in the pot. Set the bacon aside.

Heat the olive oil in the same pot over medium heat and cook the onion, celery, carrot, and garlic until soft, about 6 – 7 minutes, stirring. Stir in thyme until fragrant, about 1 minute.

Sprinkle in the flour and stir gently until lightly browned, about 1 minute. Gradually whisk in the milk, vegetable stock, clam juice and bay leaf, and cook, whisking constantly, until slightly thickened, about 1-2 minutes. Add the ouzo and cook until the alcohol steams off.

Stir in the potatoes. Bring to a boil; reduce heat and simmer until potatoes are tender, about 15 to 20 minutes. Add the clams and the chunks of fish if using. Simmer for 6 – 7 minutes, then add the remaining seafood (mussels and shrimp or scallops if using instead of the fish). Add the heavy cream and cook for another 6 – 7 minutes. Season to taste with salt and pepper. If the soup is too thick, add more milk as needed until desired consistency is reached.

Serve immediately, garnished with crumbled bacon, if desired.