Combine all ingredients in a blender and process until thoroughly blended. Can be made a day in advance and kept refrigerated.
For the Garlic herb butter:
Combine all ingredients in a small mixing bowl and mash with a fork until evenly blended. Can be made a day in advance and kept refrigerated.
For the Bread:
Preheat oven to 450º F with rack in the middle of the oven.
Wash tomatoes and remove the core, then cut into ¼" slices. Lay the slices in a glass dish and pour the marinade over them. Set aside while preparing the bread.
Slice bread lengthwise with a serrated knife to create a top and bottom. Spread half of garlic herb butter on the cut surface of each half of the bread.
Place bread, cut side up, on a sheet pan. Place in the oven for 3-4 minutes until the bread is lightly toasted. Remove from oven.
Lift tomato slices from the marinade and drain. Lay slices, slightly overlapping, on the toasted bread. Sprinkle with Parmesan cheese. Return to the oven for 1-2 minutes to just melt the cheese. Remove from oven and transfer to cutting board.
Cut each half loaf, crosswise, into 8 pieces. Sprinkle with sliced basil leaves and arrange on a warm serving platter. Garnish with a fresh sprig of basil.