In a bowl, combine minced beef, cooked rice, egg, salt, and pepper. Divide the mixture into 16 equal portions.
Wet your hands with water. Take one portion, flatten it in your palm, place a piece of sheep cheese in the center, and form it into a ball. Repeat with the remaining portions.
Heat oil and butter in a large pan over medium-high heat. Fry the meatballs for 2-3 minutes until browned on all sides.
Transfer the meatballs to a baking dish. Bake at 180°C (350°F) for 10 minutes until cooked through.