Make the kubbeh filling: Place the 1 chopped onion in a clean kitchen towel. Working over the sink or a bowl, squeeze out and discard as much liquid as possible. Place the onions in a large bowl. Add the beef to the large bowl along with the salt, pepper, baharat, and chopped celery leaves, if using. Mix with your hands until combined, then cover the bowl and refrigerate for 30 minutes.

Make the kubbeh patties: Mix together  3 cups semolina flour, 1 cup water, 1 teaspoon salt, and  1 tablespoon oil in a medium bowl until smooth. Knead the mixture in the bowl to combine until it forms a dough that is moist but not sticky. If dough feels sticky, knead in additional semolina flour, 1 teaspoon at a time. If dough feels dry, add additional water, 1 teaspoon at a time.

Line 1 to 2 sheet pans with parchment paper. Shape the kubbeh: pinch off small pieces of dough, weighing them out to 30 grams each, about half the size of a golf ball. Keep the dough covered with a damp towel or paper towel while working, so it doesn't dry out. Shape each piece into a ball, then flatten out into flat, thin rounds. Place a little less than a tablespoon of meat in the center of the dough and bring the sides around it and pinch to seal. Pick it up and roll it between your palms to form into a smooth ball. Place on the prepared sheet pan, cover again with a damp towel, and repeat rolling, filling and shaping until the remaining kubbeh filling and  dough have been used.

If planning to cook these kubbeh within 12 hours, place in the refrigerator; if waiting longer, freeze the kubbeh on the sheet pan until solid, about 2 hours, then transfer to an airtight container and freeze until ready to cook.

Make the soup: In a large stockpot, heat 1 tablespoon of oil over medium heat. Saute the 1 chopped onion until translucent, about 4 minutes. Add the grated beets and saute until softened, around 2 minutes. Add the tomato paste and stir, mixing, until the mixture is fragrant and thickened, about 1 minute.

Add the rest of the beets and saute until softened, about 7 to 8 minutes. Add the celery, sugar, salt, water, half of the lemon juice, and bring the mixture to a boil. Season with the black pepper. Gently drop the kubbeh into the soup, reduce the heat to low, and cover the pot. Simmer until the kubbeh and the beets are cooked through, about 50 minutes.

Season the soup with more salt and pepper to taste. Add remaining lemon juice and serve the soup with a few kubbeh per serving immediately.