These rice-and-meat-stuffed bundles are a traditional Greek appetizer.
Heat oven to 325 degrees. In a bowl, combine onion, rice, lamb, beef, garlic, parsley, carrot, lemon zest, 1 tablespoon oil, chopped mint, salt, and pepper.
Place a leaf, vein side up, on a work surface; place about 1 tablespoon filling just below center. Fold bottom of leaf over filling and sides in toward center; roll up. Do not overfill or roll too tightly. Repeat, making 35.
Lay dolmades, seam side down, in a 9-by-13-inch glass baking pan; do not pack tightly.
Combine stock and remaining 3 tablespoons oil; pour over dolmades. Squeeze lemon over dolmades, and place lemon slices and mint sprigs on top. Place another 9-by-13-inch baking pan, half full of water, on top to weigh down dolmades.
Bake for 40 to 50 minutes. Let dolmades cool in cooking liquid, still weighted, for 2 hours. Serve drizzled with olive oil, or refrigerate for up to 2 days; bring to room temperature before serving.