Defrost the puff pastry slices side by side. Peel and thinly slice the onion. Wash the rosemary, shake dry and remove the needles. Peel and wash the potatoes and cut or slice them thinly.
Heat the oil in a large frying pan. Fry the potato slices for 4-5 minutes while turning them over until golden brown. Add the onion slices and rosemary about 1 minute before the end of the cooking time, season with salt and pepper. Sprinkle the potato slices with sugar, let them caramelize slightly and then deglaze with vinegar. Put the potatoes into a well greased dish (approx. 23 cm Ø)
Place the puff pastry slices on top of each other and roll out round on a floured work surface (approx. 25 cm Ø). Place the puff pastry on top of the potatoes and fold in any protruding edges. Prick 4-5 times, then bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes until golden brown
Remove the tart from the oven, remove from the edge and immediately and carefully turn over onto a plate. Cut the tarte into pieces and serve
On eight pieces: