Wipe out the pot with a damp paper towel and return to medium heat. Melt the butter. Add the second half of the leek, fennel, and onion, and sauté until softened and translucent. Stir in the garlic and cook for 30 seconds or until fragrant.
Add the chopped tomatoes to the vegetables. Continue to cook until the tomatoes start to break down.
Stir in the wine and bring to a gentle simmer. Cook for about five minutes, or until reduced.
Add the dried thyme, paprika, and saffron, stir well to combine, and let the flavors meld together for 2 minutes. Stir occasionally to prevent burning.
Pour the strained, homemade seafood broth back into the pot and bring to a low boil.
Add the clams and mussels to the pot, first. Cover, and cook until they begin to open (approximately 5-10 minutes). Discard any clams and mussels that do not open. Add the fish and cook for 5 minutes, gently mixing to combine. Next, add the scallops and shrimp, and cook, covered, for 5 minutes.
Taste and adjust the seasoning with salt and black pepper to taste.
Garnish with freshly chopped parsley and serve with crispy baguette slices if desired.