If using fresh leaves, blanch a bunch at a time in boiling water for 10-15 seconds until they change color. Transfer them to a bowl of cold water.
If using jarred leaves, wash them thoroughly to remove the pickling liquid. They are then ready to use.
Filling
Chop the herbs very finely, preferably using an electric chopper.
Grate the garlic cloves, carrots, and tomatoes finely, or chop them very finely using an electric chopper.
Wash the rice very well until the water runs clearer.
In a large bowl, mix the herbs, garlic, carrots, tomatoes, salt, sumac, and olive oil. Taste the liquid at the bottom of the bowl; it should be a little saltier than you would usually like. If it's not slightly too salty, add more salt. Remember—the rice expands a lot and requires a good amount of salt.
Stuffing the Leaves
Lay the leaf with the bottom side, where the veins are more noticeable, facing up. Place two teaspoons of filling in the bottom middle part of the leaf. Do not overfill, as the leaf may tear once the rice cooks.
Fold both sides.
Fold the bottom.
Finish rolling the leaf from bottom to top. Do not roll too tightly; leave room for the rice to expand.
Assembling the Pot
Layer the bottom of the pot with either leaves or tomato slices. Whichever you choose, make sure to cover the bottom well to protect the bottom layer of stuffed grape leaves from burning.
Place the rolled leaves close to each other so they keep their shape during cooking.
Sauce
Once you've finished filling your pot with layers of stuffed grape leaves, mix the water, pomegranate syrup, and lemon juice, then pour it over the leaves. You don't want the water to completely cover all the leaves—just enough to almost cover the last layer. The vegetables in the filling will release liquid while cooking, and the steam created within the leaves will help cook the rice.
Cooking
Cover the pot and bring it to a boil on the stove. Once boiling, bake at 180℃ (350℉) for 20-25 minutes. Then reduce the temperature to 130℃-140℃ (260℉-280℉) and bake for another 45 minutes to 1 hour.
Notes
I like to wait until the stuffed grape leaves cool down a little and eat them with tzatziki. I made a quick tzatziki by mixing some grated garlic with yogurt and grated cucumber (that I salted and squeezed to keep crunchy).