In a smaller pan sauté the finely chopped onions in vegetable oil over low heat, stirring frequently, until translucent. Do not let them burn. Salt lightly to help tenderize them.
Half of the cooked onions goes in the pot that you are using to make the stuffed peppers.
Mix the rest of the onions with sweet paprika powder, add as much that gives a nice red color to the onions. First add a flat teaspoon. Add more if needed. Make sure that the pan is not on the heat when you are adding the paprika, otherwise your paprika burns and becomes bitter.
Combine the ground pork, the egg, the uncooked rice, the minced garlic, the sautéed onions mixed with paprika, ground black pepper and salt to taste. Mix well.
Wash the peppers. Cut off the tops and remove the seeds. Fill the peppers with the meat mixture. Be sure to leave some room, as the rice will expand when cooked. IPour the tomato juice (1.5 liters) or tomato puree (1 liters) over the cooked onions. If you are using tomato puree, then add 2 cups of water to make it thinner. Bring it to a boil, lower the heat, place the stuffed peppers and the meatball is the tomato juice and slowly cook for about 50 minutes. f you have leftovers, shape meat balls in the palm of your wet hands.
Meanwhile, you have time to make the roux (to thicken your tomato sauce): In a pan, heat 4 tablespoons of oil, add 2-3 tablespoons of flour, stirring constantly. You need just enough flour to make the consistency of your roux not too thick and not too thin. It should spread out in your pan and bubble a little.
After 2-3 minutes of searing, when it starts to brown, take it off the heat, allow to cool.
Peel the potatoes and cut them into bigger chunks. In a medium pot heat water, salt it and boil the potatoes until tender, then drain them.
When the stuffed peppers and meatballs are cooked, gently take them out from the pot.
Mix your roux with a little cold water to thin it, this way you avoid lumps when you pour back the roux to the tomato liquid to thicken it a bit. First pour back only the half of your roux, bring it to a boil. The tomato consistency should be like a thiner cream soup. Add more roux if needed to get this consistency. Add 1-2 tablespoons of sugar and celery leaves (optional).
Place back the stuffed peppers and the meatballs in the tomato sauce and slowly simmer it for another 2-3 minutes.
Serve with boiled potatoes.