Preheat the oven to 300°. In a large, deep skillet, bring the verjus to a boil. Add the clams, cover and cook over high heat, shaking the pan occasionally. As the clams open, after about 4 minutes, transfer them to a deep, ovenproof platter. Discard any clams that do not open. Cover the platter with a damp kitchen towel and keep the clams warm in the oven. Reserve the clam cooking liquid in a bowl and wipe out the skillet.
Heat the olive oil in the skillet. Add the garlic and shallot and cook over moderate heat, stirring, until softened, about 4 minutes. Pour in the reserved clam cooking liquid, stopping before you reach the grit at the bottom. Boil over high heat until reduced to 1 cup, about 5 minutes. Add the tomato and parsley and season with salt and pepper. Pour the sauce over the clams and serve right away.
For a wine match, consider a New Zealand Sauvignon Blanc, which has a peppery zip that would work well here.