Line a baking sheet with parchment paper and brush it lightly with olive oil. Spread the thawed puff pastry squares on the tray. Place the edges a little on top of each other and press firmly.
Sauté the onions and garlic with a little olive oil and sauté over a low heat for approx. 20 minutes. Add sugar and vinegar, season with salt and pepper.
Spread the onions on the dough. Cover evenly with anchovies and olives and sprinkle with the marjoram. Bake at 220 C for approx. 20-25 minutes until golden brown.