Thaw out 1 puff pastry sheet. Prick the middle with a fork. Brush puff pastry sheet with olive oil.
Cut the potatoes into thin rounds and layer them on top of the puff pastry sheet. Fold edges of puff pastry in around the potatoes. Season with salt and sprinkle with nutritional yeast (optional) and break off some rosemary twigs and scatter over potatoes.
Bake in oven at 200 C for about 20 minutes or until potatoes are cooked and slightly crispy around the edges and the puff pastry has cooked through.