Preheat oven to 180C/160C fan/gas 4.
Roll out the pastry on a lightly floured surface until 5mm thick. Roughly cut 2 rectangles measuring 15cm x 18cm from the pastry and place on baking trays lined with non-stick baking paper. Top the pastry with the caramelised onion leaving a 2cm border around the edge. Arrange the potato, feta and pancetta over the onion and sprinkle with rosemary, salt and black pepper.
Bake for 25 minutes or until the tarts are puffed and golden. Serve with a simple rocket salad.⏱ 25 min