Add rice to a medium bowl and water to cover. Swish and gently rub with your fingers to rinse the rice. Drain off water and repeat two to three times. Drain and set aside.
To make the sumac water for the sauce: add ground sumac to a small bowl and pour 2 cups hot water over it. Stir and set aside to infuse.
Prepare cabbage
Bring a large pot of water to a boil. (*Footnote 5) Add the salt. Cut a 1/2" (1 cm) deep X in the stem end of the cabbage and add it to the water. If using two cabbages, cook them one at a time. Bring the water back to a boil, partially cover the pot, and cook the cabbage until a knife inserted to its core meets no resistance, 12 to 15 minutes. Flip the cabbage 1 to 2 times if it’s not fully submerged in the water. Do not let the cabbage cook so long that it becomes mushy.
Meanwhile, prepare an ice bath by adding ice and water to a large bowl.
When the cabbage is cooked, plunge it into the cold water. When it’s cool enough to handle, remove it from the water, core it using a paring knife, and carefully separate the leaves, stacking them on a plate. Line the bottom of a wide 3-quart lidded pot with a layer of small and/or torn leaves. Set aside.
Make filling
Place the drained rice in a large bowl. Add the ground meat, onion, garlic, parsley, grated tomato, pepper taste, and chilies. Gently mix with your hands or a fork until the ingredients are just combined. Do not over mix. Sprinkle over the mint, red pepper flakes, salt, and black pepper. Mix again.
Assemble
Place a cabbage leaf on your work surface with the interior of the leaf facing up and the bottom of the leaf toward you. Use a sharp knife to cut out the thick stem and discard it. If the leaf is too big, slice it into two pieces so it’s easy to wrap. Place about a tablespoon of filling at the tip of the V and shape it into a log, leaving at least an inch between it and the edges of the leaf. Fold the left and right edges of the leaf over the filling, then fold the bottom flaps of the leaf up and over, and roll it away from you to make a parcel. Don’t roll the leaf too tightly--leave room for the rice to expand during cooking.
Place the cabbage roll seam-side-down in the pot and repeat until the filling is used up. Lay the rolls side by side, close together but not snug. Make two layers if necessary.
Make the sauce
Line a sieve with cheesecloth or a damp large paper coffee filter, and set it over a quart measuring cup or a medium bowl. Pour in the sumac water. Gather the cheesecloth around the ground sumac and squeeze it to release as much liquid as possible. Discard the sumac.
Pour 1 cup of the sumac water into a small bowl; add water if necessary, to make 1 cup total. (*Footnote 6)
Mix in the tomato paste, olive oil, and salt. Stir to mix well. Pour the sauce over the cabbage rolls.
Heat the pot over high heat and bring the sauce to a boil.
Lay a piece of parchment paper over the rolls and a heatproof plate on top of the paper, to keep the rolls under the sauce.
Reduce the heat to low. Cover and cook for 30 minutes. Check after 15 minutes (use tongs to lift the plate and paper) to make sure that there is still liquid in the pot. Add 1/2 cup sumac water or plain water if the bottom is nearly dry. You want to end up with just enough reduced sauce to slightly coat the cabbage rolls.
Let the cabbage rolls rest, covered, for at least 10 minutes.
Serve hot or warm.
Store the remaining rolls in the fridge for 3 to 4 days. The leftovers will taste even better.