How to Make It
Preheat the broiler. In a large, ovenproof nonstick skillet, heat the olive oil. Add the onion and garlic and cook over high heat, stirring frequently, until softened, about 5 minutes. Add the beef and cook, breaking it into small lumps, until lightly browned, about 5 minutes. Stir in the cumin and chile powder and cook for 2 minutes. Stir in the olives, raisins and capers and season with salt and pepper. Stir in the tomato sauce, stock and ketchup and bring to a boil. Simmer over moderate heat, stirring frequently, until thickened, about 10 minutes.
Make 4 shallow depressions in the picadillo and crack the eggs into them. Broil 6 inches from the heat for about 4 minutes, until the whites are set and yolks are still runny.
Meanwhile, spread the cut sides of the buns with the butter and broil until golden. Transfer the buns to plates, spoon the picadillo and eggs on top and serve.