In a medium bowl, whisk the lemon juice with the shallot and crème fraîche. Gradually whisk in the olive oil and season with salt and pepper. Whisk in the diced fennel and chopped fennel fronds.
Preheat the broiler and position a rack 6 inches from the heat. Arrange the shrimp, lobster tails and oyster shell halves in a roasting pan in a single layer. Place the scallops in the 6 flattest oyster shells. Place the oysters in the remaining shells. Spoon 3/4 cup of the vinaigrette over the seafood, being sure to coat them completely. Season with pepper and broil until lightly browned, about 7 minutes. Transfer the seafood to plates and drizzle with some of the vinaigrette, passing the toast and any remaining vinaigrette at the table.
A zesty Australian Riesling will highlight the seafood’s sweet, briny flavors.