To prepare the sauce, heat the margarine in a medium saucepan set over medium heat until melted. Add the chopped onions and cook, stirring, until soft and lightly browned, about 10 minutes. Add the brown sugar and tomatoes, crushing them with your fingers as you add them to the pan (with their juice), and tomato sauce and lemon juice. Stir, bring to a boil, then reduce heat to low and cover. Cook, stirring occasionally, for 1 1/2 hours.

Preheat the oven to 350°F. Lightly grease a large, nonreactive baking dish and set aside.

Prepare Cabbage
While the sauce cooks, prepare the cabbage. Using a paring knife, cut a cone-shaped incision in the bottom of the cabbage to remove the core. Place the cored cabbage into the boiling water, reduce the heat, and simmer, 15 minutes. Drain, cover with cold water and Drain again. When cool enough to handle, peel off the leaves, trying not to tear them. Trim thick ribs from the leaves. You should have 16 to 20 relatively intact leaves. Set aside.

Prepare Filling
To prepare the filling, combine the ground beef with the grated onion, eggs, rice, and ketchup; season with salt and pepper. Mix by hand, adding up to 1/2 cup of water if necessary, until mixture is moist but still thick.

Make Rolls
Place about 1/4 cup of the meat filling in the center of each leaf. Fold the bottom of the leaf over the filling, Fold in the sides, then roll to enclose securely. Repeat with the remaining filling and cabbage leaves. Arrange the packages, seam side down, on the prepared baking dish. Sprinkle with the prunes and raisins and spoon the tomato sauce over top. Cover the baking dish and bake for 1 1/2 hours.