Preheat oven to 200C, Fan 180C, Gas 6.
In a large roasting tin mix together the oil, garlic and vegetables with the rosemary. Season with a little salt and pepper and roast in the for 20-25 minutes or until tender and starting to brown. Allow to cool slightly.
Increase oven temperature to 220C, Fan 200C, Gas 7.
Unroll the puff pastry sheet on a clean work surface and cut in half to give two even sized rectangles. Place one of the rectangles on a baking tray.
Spoon the Oven Roasted Mushroom Pate over the pastry sheet on the baking tray, leaving a 2cm border all round. Scatter the roasted vegetables evenly over the pate, and brush the edges of the pastry with a little cold water. This will help to seal the top to the base.
Fold the remaining pastry rectangle in half along the longest length and using a sharp knife make cuts through the fold at 45 degree angle to the edge. Leave an uncut border of about 2cm all around.
Carefully unfold the cut pastry and place oven the vegetable mixture on the baking tray. Gently press down around the edges to seal.
Brush all over with beaten egg and bake in preheated oven for 20-25 minutes until crisp and golden in colour.