Flounder rolls with crab filling in shrimp and shellfish sauce

Ingredients:

• 4 large flounder fillets (approximately 300 g each), cut in half lengthwise, or 8 small fillets (100-150 g each)
• 0.9 kg cockles, washed with a brush
• 450 g rock shrimp
• 0.5 kg crab meat pieces, sorted
• 1 bottle (240 ml) of clam juice
• 1/4 cup olive oil
• 1 small onion, finely chopped
• 1 small fennel root, cored and finely chopped + 2 tbsp chopped fennel greens
• 3 cloves garlic, crushed
• 1 tbsp. l. dried oregano
• 0.5 tsp red pepper flakes
• 2/3 cup dry white wine
• 2 cans of diced tomatoes (800g each)
• 1 teaspoon finely grated lemon zest

Preparation:

1. Heat the olive oil in a large saucepan over medium heat. Add the onion, fennel root, and garlic and cook, stirring occasionally, until softened but not browned, 10-12 minutes. Add the oregano and red pepper flakes and cook, stirring, for 30 seconds. Increase the heat to medium-high, add the wine, and simmer until almost completely evaporated, about 5 minutes. Add the tomatoes and clam juice and simmer, stirring occasionally, until the tomatoes are softened and the broth has thickened slightly, about 15 minutes.
2. Meanwhile, in a medium bowl, combine the crab meat with the lemon zest, 1 tablespoon of fennel fronds, and a pinch of salt. Season the flounder with salt and pepper. Place 1/4 cup of the crab mixture about 2 inches from the widest edge of each fillet and roll the fish tightly into a roll. Insert a toothpick or small wooden skewer into the center of the roll to secure it.
3. Carefully place the flounder rolls into the simmering tomato broth. Cover and cook until the fish is opaque, 12-15 minutes. Using a slotted spoon, transfer the rolls to a rimmed serving platter and remove the toothpicks; cover with foil.
4. Add the cockles to the simmering tomato broth, cover, and cook until they begin to open, about 6 minutes. Stir in the shrimp and cook until they are opaque and the clams are fully open, about 2 minutes more (discard any unopened shells). Pour the sauce with the clams and shrimp onto the platter with the fish rolls and sprinkle with the remaining 1 tablespoon of fennel fronds.