On a cutting board, finely chop the onion for the meatballs using a sharp knife and coarsely grate the green apple on a grater.
In a large bowl, put the onion, green apple and the rest of the ingredients for the meatballs, the ground chicken, melted butter, eggs, bread crumbs, salt and freshly ground pepper and knead well. Allow the ground meat to rest while making the sauce.
For the sauce, heat up a deep non-stick skillet on high heat and then add the 2 tbsp olive oil and the 2 tbsp butter.
Saute the leek for 2-3 minutes, until it starts to soften, stirring constantly so it does not brown.
Add the tomato paste and the sweet paprika and continue to saute for 1 more minute.
Pour in the sweet red wine, add the grated tomato with the chicken broth, the brown sugar, the fresh oregano sprigs and sprinkle with salt and freshly ground pepper.
Bring the sauce to a boil and then lower the heat and allow the sauce to simmer.
Knead the ground chicken into small meatballs, put a non-stick skillet on high heat and pour in some olive oil to heat up.
Cook the meatballs in the skillet on all sides until brown and then place them in a Pyrex dish.
Pour the sauce over the meatballs in the Pyrex dish and cook in a preheated conventional oven at 180ο C, for 25-30 minutes.
While the meatballs are cooking in the oven put some salted water in a saucepan on high heat and boil the rice for 10 minutes.
Once the rice is ready, strain it, put it back in the saucepan, add the butter and mix well.
When the meatballs are ready, remove them from the oven and serve on plates with the meatballs and sauce spooned over the rice.