Heat a 12-inch heavy skillet over high heat until hot, at least 2 minutes. Meanwhile, pat lamb dry and rub meat all over with salt and pepper. Add oil to hot skillet, then brown racks, in 2 batches if necessary, on all sides (not ends), about 10 minutes per batch.
Transfer 2 browned racks aside for later preparation.
To prepare the filling:
Combine raw minced lamb, rice, parsley, mint, oil, spices and salt in a medium bowl until well combined.
To assemble the grape leaves:
If using fresh leaves, bring a pan of salted water to a boil, add the leaves, and blanch for 3 minutes. Remove from the pan and put them in a sieve to cool. If using leaves preserved in brine, soak them in hot water for 15 minutes, then drain, and pat dry with paper towels (if needed).
Lay 1 grape leaf flat on a work surface or a flat, put a spoonful of the filling on top, fold the sides and carefully roll up the leaf into a cigar shape. Repeat with the remaining leaves and filling until 40 leaves have been used.
Put the remaining unrolled leaves in the bottom of a large pan, then 2 pieces of brown racks. Place about half of the stuffed grape leaves in one tight layer in the pan, then put the other 2 brown racks in the middle. Make other layers of grape leaves.
Drizzle with olive oil, lemon juice and season with salt (to taste). Position a plate snugly on top of the leaves and pour in 1 cup of boiling water to cover.
Bring to a boil, then reduce the heat and simmer for 50 - 60 minutes. Carefully lift out the grape leaf rolls with a slotted spoon and serve warm in a round shaped plate.