Preheat the oven to 425 degrees F. Whisk the olive oil, minced garlic, lemon zest and juice, anchovies, basil, parsley, paprika and 1 teaspoon salt in a large bowl. Add the shrimp, tomatoes, scallions and jalapeno; toss.
Tear off eight 16-inch sheets of parchment paper. Make the packets (see photo gallery), using a double layer of parchment for each packet: Arrange about one-quarter of the shrimp mixture on a double layer, using a slotted spoon. Top with 2 tablespoons clam juice, 1/2 tablespoon butter and one-quarter of the liquid from the bowl. Seal as directed. Repeat to make 3 more packets; divide between 2 baking sheets.
Transfer to the oven and bake until the parchment puffs and the shrimp are just cooked through, about 20 minutes. Let rest 5 minutes before opening.
Meanwhile, toast the baguette slices in a grill pan until marked; rub with the remaining garlic clove. Carefully open the packets and serve with the grilled bread. Photograph by David Malosh
Be careful when opening parchment packets - the steam is hot!