Preheat oven to 200ºC (180º for fan assisted ovens)/400ºF/ Gas M6
Place prepared vegetables on large baking sheet, drizzle with olive oil, and scatter with rosemary and salt & pepper to season. Roast for 15-18 minutes or until just tender. Allow to cool. Increase oven temperature to 220ºC (200º for fan assisted ovens)/425ºF/ Gas M7.
Unroll the pastry sheet and cut in half across length to give two rectangles. Lay one on a lined baking sheet. Place the vegetables on pastry in an even layer leaving a border of approx. 1.25cm/½" all round.
Fold the second pastry sheet in half down its length and using a sharp knife make cuts down the folded side, at 90º to the edge towards the opposite side, BUT leave a border of 1.25cm/½" down that side and at the short ends.
Brush base pastry border with beaten egg, open out second pastry sheet and lay over base, press edges together, trim off with a sharp knife and knock up edges to seal well. Brush top with beaten egg and scatter over a little more rosemary. Bake for 20 -25 minutes until risen and golden brown.