Using a sharp knife, make 3 1/4" deep, 2 1/2" long diagonal cuts in skin of each fish fillet. Arrange fillets in a single layer, skin side up, in a 15"x10"x2" glass baking dish. Pour sherry and 1/4 cup olive oil over fish; sprinkle with pepper. Cover and refrigerate at least 4 hours and up to 6 hours, turning every so often.
Preheat oven to 425*F. Combine butter and garlic in a heavy medium saucepan. Cook over medium heat till butter melts and garlic begins to brown, about 12 minutes, stirring occaionally. Discard garlic cloves. Add panko to butter(mix will bubble); cook till golden brown, about 3 minutes. Add the lemon juice; remove from heat. Stir in smoked paprika. Season sauce to taste with salt and pepper. Cover to keep warm while preparing fish.
Remove fish from marinade and drain. Sprinkle fish with coarse salt. Heat remaining 1 tbls. oil in a large ovenproof skillet over medium high heat. Add the fish, skin side down, and cook until lightly browned, about 1 minute. Turn fillets over; place skillet in the oven and roast until fish is just opaque in center, about 2 minutes.
If serving with Roasted Sweet and Sour Onions, spoon the onions into the center of 6 plates. Top each serving with 1 fish fillet. Spoon sauce over and serve. Enjoy!