Brown onion in a little butter. Place all filling ingredients into a food processor and process until well combined and there are no chunky bits. I use my Braun hand-held blender's chopper jug attachment for this. Add half the egg, breadcrumbs and mix in well. Set aside.

Preheat oven to 220C (200C fan forced, 425F, Gas mark 7).

Thaw puff pastry sheets for about 4 minutes. Cut pastry in half and place on the bench top with the longer edge closest to you.

Spoon filling along the middle of the rectangle, pressing down firmly with your hands. Roll up the pastry to enclose the filling and form a log. Make sure that there is about a 1cm overlap at the pastry closure. Place seam side down on a cookie sheet lined with baking paper.

Brush with egg wash and sprinkle with sesame seeds. Cut each log into 4 with a bread knife - trying not to squash them down.

Bake for about 15 minutes, or until the pastry is puffed and golden. Serve with tomato sauce or green tomato relish.