Preheat oven to 200 degrees celsius. Line two baking trays with baking paper and set aside.
Lay the puff pastry sheets onto the bench and allow to defrost.
Finely chop the onion and place into a large bowl.
Add the chicken mince, breadcrumbs, egg, grated cheese, salt and pepper. Mix until well combined.
Stir through the corn kernels.
Cut each pastry sheet in half. Spread one-eighth of the mixture along the middle of each pastry half.
Brush the whisked egg along one side of the mixture.
Roll the pastry over the mixture, placing the seam face-down. Cut the roll into 3 equal pieces.
Place onto the baking tray, lightly brush the milk over the pastry and sprinkle with sesame or poppy seeds.
Repeat with remaining mixture and pastry sheets.
Bake in the oven for approximately 25 minutes or until golden and cooked through.
Leave to cool on the trays for 5 minutes before transferring to a wire rack to cool completely.
Serve immediately or store in an airtight container in the freezer for up to 3 months.