Soak rice in cold water, and drain. In a large bowl, mix together the lamb mince, rice, allspice, salt and pepper until well blended. Place about 1 tablespoon of the meat mixture onto the centre of each leaf. Fold the leaf over once, turn in the edges on each side, and then roll the leaf closed.
Stack the dolmades in a large pot, covering each layer with slices of garlic. Add just enough water to cover the rolls, then pour in the lemon juice. Add the olives to the pot for flavouring, if desired. Place a plate on top of the rolls to keep them under water.
Bring to a boil, then reduce heat, cover and simmer for 1 hour and 15 minutes. Check the rice for doneness.
Do not stack the rolled grape leave more than 3 or 4 layers thick in the pan. More layers can make the rolls cook unevenly; the ones on the bottom may overcook before the ones on the top are done.