Thaw puff pastry. Peel the onion and garlic, chop finely and saute in hot olive oil in a pan. Saute ground beef and cook, then stir in tomato paste and season with salt, pepper and rosemary seasoning. Remove from heat and let cool.
Drain mozzarella and cut into thin slices. Roll out thinly puff pastry successively. Grease ramekins and line with the dough, place extra dough aside. Mix crème fraîche and eggs with the ground meat mixture. Spread the filling in the molds and cover with mozzarella slices. Cut out 8 cm (approximately 3 inch) circles from the remaining dough and place on top. Brush with beaten egg yolk. Bake in a preheated oven (180°C) (approximately 350°F) for about 30 minutes until golden brown.