Prepare bulgur according to package directions; transfer to a medium bowl.
Preheat oven to 325°F.
Bring 2 1/2 cups water to a boil in a large skillet. Trim bottom of cabbage and separate leaves. Add the 8 largest leaves to the boiling water, cover, reduce heat to medium-high and simmer until softened, 5 to 7 minutes. Transfer to a clean work surface to cool. Reserve the remaining leaves.
Meanwhile, heat oil in a large skillet over medium heat. Stir in onion and leeks. Cover and cook, stirring occasionally, until the vegetables are soft, 5 to 8 minutes. Stir in salt, pepper, turmeric, ginger, allspice and cinnamon; cook, stirring, 1 minute more. Transfer the mixture to the bowl with the bulgur and let stand until cool enough to handle, about 5 minutes. Add the lamb, parsley, mint and lightly beaten egg. Gently knead the mixture with your hands until well blended.
Line a 9-by-13-inch baking pan with some of the uncooked cabbage leaves. Place about 1/2 cup of filling over the root end of each cooked leaf. Fold in the sides and roll up to form a bundle. Lay the cabbage rolls seam-side down in the pan. Combine wine, broth, lemon zest and 2 tablespoons lemon juice. Pour over the cabbage rolls. Cover tightly with foil.
Bake until the thicker ribs of the cabbage leaves are very tender and an instant-read thermometer inserted into a roll registers at least 165°F, 45 minutes to 1 hour.
Transfer the rolls and cabbage leaves to a serving platter; tent with foil to keep warm. Carefully pour the juice from the pan into a small saucepan; bring to a boil over medium-high heat and boil until reduced by about half, 6 to 10 minutes. Whisk the remaining 1 tablespoon lemon juice and egg yolk in a small bowl. Whisk the reduced liquid into the lemon-yolk mixture, then pour the sauce back into the pan. Cook over low heat, whisking constantly, until thickened enough to coat the back of a spoon, 2 to 4 minutes. (Take care not to overheat the sauce or the egg will curdle.) Serve the rolls with the sauce.
TIPS & NOTES
Make Ahead Tip: Prepare cabbage leaves (Step 3); make stuffing (Steps 1 & 4), omit egg; refrigerate separately up to 1 day. Add egg and continue with Steps 5-7.
Per serving: 521 calories; 30 g fat (11 g sat, 15 g mono); 155 mg cholesterol; 38 g carbohydrates; 0 gadded sugars; 24 g protein; 11 g fiber; 642 mg sodium; 953 mg potassium.