Dough
Filling
Sauce
Combine the flour and salt in a mixing bowl. Add the egg and water, mixing well with your hands. Add more water, if needed, to form a soft dough. Cover and set aside for at least 30 minutes.
Combine the onion, ground beef, salt, and pepper; mix well.
Divide the dough into two portions and lightly flour a work surface. Keep one piece of dough covered while you roll out the second portion into a rectangle, rolling the dough as thin as you can. Cut the rectangle into 2-inch squares with a knife or pastry wheel.
Place about a teaspoon of the meat filling in the center of each square. Seal the dumplings by gathering the edges of the dough and pinching them together at the top to form a bundle. Transfer the finished dumplings to a floured plate, and sprinkle more flour over the dumplings to prevent sticking. Repeat with the second piece of dough.
Bring a large pot of salted water to a boil over medium-high heat, and cook the dumplings until the dough is tender, 20 to 25 minutes. Remove the dumplings and some of the cooking liquid from the pot with a ladle , transfer onto a deep serving platter.
Combine the yogurt and garlic set aside.
Heat the oil, red pepper flakes, dried mint and sumac in a small skillet over low heat just until the pepper flakes have started to color the oil; don't let them burn. Remove from the heat and keep warm.
Pour the yogurt on the dumplings, garnish with the oil spice mix. Serve the manti immediately.