These small red potatoes quickly absorb the rich Provencal flavors of garlic, olives, thyme, and rosemary while steaming.
Heat oven to 400 degrees. Place potatoes, onions, garlic, tomatoes, and olives in a medium bowl. Add olive oil, salt, and pepper and toss to coat vegetables.
Fold parchment piece in half, cut into a half-heart shape, and open. Place vegetable mixture on parchment, 2 to 3 inches from the crease, and scatter rosemary and thyme sprigs on top. Fold the other half of parchment over the ingredients. Make small overlapping folds to seal the edges, starting at the top of the heart.
Two inches from the end, twist the parchment twice, gently but firmly, to seal the packet. Place packet on a baking sheet and bake for 30 minutes. Remove from oven and open packet. Use your fingers to crumble the herbs, discarding the stems. (Don't worry about burning your fingers; the sprigs will have dried during cooking and the leaves will come off the stems easily.) Carefully pull off the skin of the tomatoes, which will have loosened. Using a fork, break up the tomatoes and stir into the potatoes. Serve immediately.
The potatoes can be cooked in a small roasting pan, if desired; toss in 1 tablespoon oil, and cover with aluminum foil.