Steps:

• Heat oven to 425 degrees. In a large bowl, combine kelp with 4 cups of cool water and let stand until softened, about 5 minutes. Reserve 2 cups of the kelp water.
• On a lightly greased rimmed sheet pan, arrange half of the softened kelp in the center, allowing excess water to drip off kelp and slightly overlapping the pieces. (Do not squeeze water out of the kelp). Rub halibut with 2 tablespoons of oil and season with salt. Set halibut in the center of the kelp and lift kelp over the sides of the fish. It should stick to the fish. Top halibut with the remaining kelp, slightly overlapping, and tuck the kelp loosely underneath the fish to enclose it.
• Roast halibut until just opaque in the center, about 15 minutes. A metal cake tester or skewer inserted in the center of the fish should feel warm to the touch. Transfer wrapped halibut to a serving platter.
• Meanwhile, in a large pot, combine clam juice and the reserved kelp water, and bring to a boil over high heat. Add mussels, cover and cook until mussels open, 2 to 3 minutes; begin checking mussels at 2 minutes and transfer them to a bowl as they open (discard any that do not open). Tent with foil to keep warm. Pour mussel broth into a separate bowl, leaving behind any grit in the pot, and reserve the broth. Rinse out pot to remove any grit.
• Combine 1 tablespoon of the lemon juice with the saffron in a small bowl and mix well. In the rinsed pot, heat the remaining 2 tablespoons oil over medium. Add shallots and cook, stirring occasionally, until softened, about 3 minutes. Stir in garlic until fragrant, about 1 minute. Add reserved mussel broth (and any juice that has drained from the mussels) and saffron-lemon juice, and bring to a boil over high. Reduce heat to medium-low and simmer gently to allow flavors to meld, about 5 minutes. Discard garlic.
• While whisking constantly, add butter 1 tablespoon at a time, blending in each addition before adding the next. Then, whisk in heavy cream. Gently simmer until sauce is slightly reduced, about 5 minutes longer. Stir in the remaining 1 tablespoon lemon juice, parsley and tarragon, and season with salt. You should have about 2 cups of sauce.
• Remove the top layer of kelp to reveal halibut. You can serve the kelp to eat with the fish or discard it. Arrange mussels around halibut, removing the top shells for easier eating if you’d like. Spoon some sauce over the mussels and fish, and garnish with parsley and tarragon.
• To serve, divide the fish and mussels among plates. Garnish with more parsley and tarragon. Serve with the remaining sauce on the side.

Steps:

• Combine octopus, bay leaf, thyme, peppercorns, 1 teaspoon salt, garlic and 1 lemon, cut in half, in saucepan along with water to cover. Turn heat to medium, cover, and bring to boil. Adjust heat so that liquid simmers slowly, and cook until octopus is tender, for 30 to 90 minutes, depending on whether you're using two smaller octopuses or 1 larger one (check for doneness with point of sharp knife). Drain, discarding everything but octopus. (You can prepare this 24 hours in advance up to this point; cover, and refrigerate octopus.) Set aside.
• Start charcoal or wood fire, or preheat gas grill; fire should be quite hot. Grill rack about 4 inches from heat source. Cut octopus into large serving pieces, brush it with half the olive oil, and sprinkle it with salt and pepper. Grill it quickly until outside browns but inside is not dried out. Cut remaining lemon into wedges.
• Brush octopus with remaining olive oil. Serve with lemon wedges, hot or at room temperature, garnished with parsley.