Start by heating olive oil in a large pot over medium heat. Add chopped onion and sliced leek, cooking until soft and fragrant. Stir in garlic and let it cook briefly to release its aroma without burning.
Add tomatoes, saffron, thyme, bay leaf, and orange zest to the pot. Stir everything well so the spices blend into the vegetables. Let this mixture cook for a few minutes to deepen the flavors.
Pour in seafood stock and white wine, stirring gently to combine. Bring the mixture to a gentle boil, then reduce to a simmer. Allow it to cook for about 20 minutes so the broth becomes rich and infused.
Add the firm fish pieces first, letting them cook for a few minutes. Then add shrimp and shellfish, covering the pot until the shells open and seafood is fully cooked. Avoid overcooking to keep everything tender.
Taste the broth and adjust salt and pepper as needed. Remove the bay leaf and sprinkle fresh parsley on top. Serve hot with crusty bread for dipping into the flavorful broth.