Savoy cabbage leaves are filled with a flavorful mixture of ground lamb, brown rice, pine nuts, dried currants, and fresh herbs, then neatly folded into rolls and baked in a sweet-and-sour tomato sauce until tender and fragrant.
Preheat oven to 350 degrees. Bring a large, deep pot of water to a boil. Season with salt. Mix together onion, lamb, rice, pine nuts, currants, cinnamon, herbs, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper. Cover; refrigerate about 20 minutes.
Meanwhile, using a paring knife, cut out and discard core of cabbage. Plunge cabbage, top-side down, into pot of boiling water. (Use a pair of tongs to keep it fully submerged.) As leaves separate from head and become pliable, remove them and transfer to a rimmed baking sheet, 6 minutes total. Let stand until cool enough to handle, 15 minutes.
Stir together tomato sauce, lemon juice, sugar, and 1/4 cup water. Season with salt and pepper. Line a 9-by-13- inch baking dish with large cabbage leaves; spread with half of tomato mixture. Working with one remaining leaf at a time, lay flat on a work surface; with a knife held horizontally, cutting away from you, shave center rib flush with leaf. Place about 1/4 cup lamb mixture in center. Fold stem end over filling, then tuck in sides and roll to enclose. Repeat with remaining leaves (using less filling as leaves get smaller). Fit rolls snugly in dish in a single layer, seam-sides down, and top with remaining sauce. Sprinkle with garlic, season with salt and pepper, and drizzle with oil. Cover; bake 30 minutes. Spoon juices over rolls, return to oven, and bake, covered, until leaves are tender and easily cut with a knife, 55 to 65 minutes more; serve.