Make the dough: in a large bowl, mix flour and salt, add milk and butter, mix until dough is formed. Knead until smooth. Cover with a plastic wrap and refrigerate for 1 hour.Make the filling: peel the potato and boil until fork tender.Place boiled potato in a large bowl and mash until smooth. Add salt, parsley, garlic and mayonnaise. Mix until combined and smooth.Take the dough out of the fridge and roll into a 22cm (9-inch) circle.Spread potato filling in the center of the rolled dough and sprinkle shredded cheese on top.Fold the edges of the dough over the filling as sown in the video. Pinch the dough to seal it.Using a rolling pin, roll the dough gently.Melt one tablespoon of butter in a large pan, place the bread in the pan and cook until golden, flip and cook until golden on the second side.Remove from heat and serve.