Stuffed Flatbread: Potato Filling

• 3 all-purpose potatoes (such as desiree)
• 25 g (1 oz) butter

Peel and halve the potatoes. Cook in plenty of salted boiling water until tender to the point of a knife. Drain and mash well; set aside. Melt the butter in a large frying pan over medium heat. Add the onion and sauté for about 5 minutes until soft. Add the tomato paste, mashed potato, parsley, dried mint and a little salt. Mix to bind together well.