1. Boil the potatoes in salted water until very soft, about 20 minutes.
2. Drain well and mash while hot until smooth. Let cool slightly.
3. Mix in the egg, cornstarch, turmeric, and salt until you get a smooth, workable dough. Set aside.
4. For the filling: heat olive oil in a pan, sauté onion and garlic until soft.
5. Add tomato, cumin, salt, and pepper, and cook until it forms a base.
6. Add the ground beef, breaking it up, and cook until fully browned.
7. Stir in the chopped egg and olives. Cook 2 more minutes, then let cool.
8. Take a portion of potato dough in your hand, flatten it into a disc, and place a spoonful of filling in the center.
9. Carefully fold the dough around the filling, sealing it into an oval shape.
10. Dip each stuffed potato in beaten egg, then coat generously in breadcrumbs.
11. Preheat oven to 210-220°C. Place them on a wire rack set over a baking tray, spaced apart.
12. Brush or spray generously with olive oil on all sides.