Defrost the puff pastry slices. Soak the rolls in water. Peel and finely dice onions. Wash and chop the marjoram. Chop, half onions, squeezed out roll, 2⁄3 Knead marjoram, 1 egg, 1 level tsp salt and 1⁄2 tsp pepper. Form 6 balls from the mixture and fry in 2 tablespoons of oil. Cut mozzarella into slices, dab dry.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Cut dough sheets in half crosswise, place 2 on top of each other, roll out square (approx. 17 x 17 cm) on a floured work surface. Spread the cheese in the middle. Place 1 ball on each. Whip the dough over it and press it down. Place on a baking tray lined with baking paper (seam facing down). Whisk 1 egg. Brush the dough with it. Bake in the oven for 20-25 minutes.
In the meantime peel, wash and finely grate the carrot. Heat 1 tablespoon of oil in a pot. Sauté the carrot and the rest of the onions. Add tomatoes, juice and ajvar. Season with salt and pepper. Simmer for about 10 minutes. Stir in the rest of the marjoram and season to taste. Add the sauce to the meatballs.