Boil the potatoes in salted water for about 15 minutes or until tender.
Drain the potatoes and then add the onion, gammon/ham, cheese, sweetcorn, butter and pepper.
Mash gently, leaving a few chunks and mix together thoroughly.
Pre-heat the oven to 220°C.
Roll the pastry sheet with a rolling pin to stretch slightly in both directions.
Cut the sheet into 4 equal rectangles.
Divide the mixture between the rectangles placing to one side to allow the other side to be folded over.
Fold the pastry over the filling and seal with egg wash and crimp with a fork.
Brush egg wash over the turnovers and if you want a pattern use a small sharp knife to score one onto the pastry being careful not to cut it. (It’s important to score the pattern after you’ve egg washed and not before or the pattern won’t show)
Bake on a sheet of baking paper on a baking sheet for about 25 minutes until golden.
Serve with lashings of ketchup and a nice salad.