For the filling:

1. In a skillet, gently sauté the onion in the olive oil over medium-low heat until tender but not brown. Remove the onion and cooking oil and set aside.
2. Add the ground lamb to the pan and cook, breaking up into smaller and smaller pieces, until the meat has lost its pink color. Add the onion back to the pan along with the rice and mix to thoroughly coat rice. Add tomatoes and 1/4 cup water. Cook for 10 minutes or until rice has absorbed juices in the pan. Stir in the allspice, herbs, salt and pepper, mixing well. Set aside, covered, for 10 minutes before stuffing the grape leaves.

Stuff the leaves and make the sauce:

1. Open a leaf and spread it on your work surface, rough veined side up. Place a spoonful of stuffing at the base of the leaf, where the stem was attached, about 1/2 inch from the edge. Fold the bottom edge up around stuffing, then fold in each side. Roll the leaf toward the point making a bundle. Place the stuffed grape leaves in the bottom of a heavy pot. They should fit comfortably without being wedged in tightly so they can expand a little as the rice in the stuffing cooks. You can make several layers of stuffed leaves, but arrange each layer in the opposite direction from the one below.
2. Add lemon and broth to just cover the grape leaves. Set a plate on top of the grape leaves, cover the pot and simmer gently for about 30 minutes or until the rice and grape leaves are thoroughly cooked.
3. To make the sauce, combine all the ingredients together and allow to rest for 30 minutes before serving.