Preheat the oven to 240°C / 475°F / Gas mark 9.
Line an oven tray with greaseproof paper and set aside.
Bring water in a medium saucepan to the boil and cook the sweet potato for 10 minutes or until tender.
Drain well, mash until smooth then allow to cool.
In another saucepan, bring water to the boil and cook the carrots and potato until they are just before turning tender.
Add the peas and corn and cook for a further 5 minutes. Drain well.
Combine all of the vegetables with the sweet potato mash along with the cheese and egg.
Stir well and season with salt and pepper.
Sift a little flour onto a clean surface and roll out the pastry sheets.
Use a 12cm-diameter pastry cutter to cut 12 discs from the pastry sheets.
Spoon the vegetable mixture evenly onto the pastry discs.
Brush the edges of the pastry lightly with remaining egg.
Fold pastries in half to enclose the filling.
Use your fingertips to gently press together and seal.
Place on the baking tray and lightly brush with the remaining egg.
Sprinkle with sesame seeds.
Bake in the oven for 15 minutes or until golden brown and cooked through.
Remove from oven and set aside to cool.