Drain the rice and transfer it to a food processor. Pulse a few times until it reaches a fine, gritty texture, stopping to scrape down the sides as needed. The ground rice should be about the size of fine semolina. Transfer to a large bowl.

Add the ground chicken, ground beef, salt, pepper, and paprika to the bowl. Knead the mixture for a few minutes, until the rice is fully incorporated, the texture is pliable, and the mixture is a consistent light pink color throughout. Cover the bowl with plastic wrap or transfer the mixture to a large Ziploc bag and refrigerate for at least 1 hour and up to 12 hours.

Meanwhile, prepare the filling: Place a wide sauté pan over medium-high heat. Add the ground beef and break it into small pieces using a wooden spoon. Season with salt, pepper, and paprika. Once the meat is fully browned and cooked through, stir in the parsley. Transfer to a bowl and allow the mixture to cool down to room temperature.

Shape the kubbeh: Remove the shell mixture from the refrigerator. Place a small bowl of neutral oil nearby to lightly coat your hands as needed while shaping. Keep the remaining shell mixture covered with plastic wrap, or in the Ziploc bag, while rolling the kubbeh. With oiled hands, pinch off a small, ping pong ball-sized piece of the shell mixture and roll it into a smooth ball. 

Use your index finger or thumb to make a well in the center. Keeping your thumb inside the opening and your fingers on the outside, gently rotate the ball while pressing outward to thin the walls, forming a small cup.

Aim for an even thickness all around, with an opening about 2 inches wide. 

Fill the cup with 1 to 1½ teaspoons of filling, pressing it down gently with the back of a spoon.

Pinch the opening closed between your thumb and forefinger while rotating the kubbeh with your other hand, forming a pointed tip. 

Press the tip into the center, then gently roll the kubbeh between your palms to form a smooth, round ball. Place the kubbeh on a tray and continue shaping the rest. You should end up with about 40 kubbeh. Wrap the tray in plastic wrap and refrigerate until ready to use.

Prepare the soup: Place a large, lidded, oven-safe pot or Dutch oven (9 or 10 quarts) over high heat. Add 1 tablespoon of oil and sear the marrow bones on all sides until browned, about 3 minutes per side. Remove the bones and set aside. 

Add 2 tablespoons of oil and the onion, reduce the heat to medium-high, and sauté for 5–7 minutes, until golden. Add the beets, celery, tomato paste, paprika, and pepper, and sauté for 3–5 minutes. Stir in the grated tomatoes, reduce the heat to medium, return the bones to the pot, and cook for 7 minutes. Add enough water to fill two-thirds of the pot and bring to a boil. Skim off any foam that rises to the surface. Reduce the heat to a simmer, add the lemon juice, and taste and adjust the seasoning.

Gently lower the kubbeh into the soup and shake the pot to help them settle. The liquid should cover the kubbeh; if it doesn’t, add a little more water. Add the chard, bring the soup back to a boil, then reduce to a simmer. Cover and cook for 1 hour. Stir the soup gently, and cover again.  

Meanwhile, preheat the oven to 200°F.

Transfer the covered pot to the oven and cook for at least 5 hours and up to 25 hours. Serve warm.