Rinse the rice, then combine it with 3/4 cup water and a pinch of salt in a saucepan. Bring the water to a boil, reduce it to a simmer, cover, and cook until the water is absorbed and the rice is tender, about 10–12 minutes. Remove the pan from the heat, fluff the rice with a fork, and let it cool slightly.
Heat 1 tbsp oil in a frying pan over low heat. Add the onions and carrots and cook for about 10 minutes, stirring occasionally, until they are soft and tender. Remove the pan from the heat and set aside.
In a large bowl, combine the ground beef, ground turkey, cooked rice, sautéed onions and carrots, salt, and pepper. Mix gently until just combined.
Roll the mixture into meatballs. Heat a bit of oil in a deep, oven-safe skillet and brown the meatballs on all sides without cooking them through. Transfer them to a plate and set aside.
To make the creamy sauce, using the same pan heat 1 tbsp oil on low heat. Add the onions and carrots and cook them slowly for at least 15 minutes, stirring occasionally, until they are very tender and lightly caramelized.
Add the dill, puréed tomatoes, and chicken stock. Increase the heat and bring the mixture to a gentle boil.
Remove the pan from the heat and stir in the sour cream until smooth. Season the sauce with 1 tsp salt, or to taste.
Return the meatballs to the pan and spoon the sauce over them. The sauce should almost cover the meatballs. Add more stock if needed.
Cover the pan and bake the meatballs at 350°F for 40 minutes, then uncover and bake for an additional 10 minutes. Enjoy!