Place the halved onion into the Thermomix and chop on Speed 5, 4 seconds. Scrape down the sides of the bowl.
Add the olive oil and saute for 3 minutes, 100 degrees, Speed 1 (with the MC off but the splatter guard or rice basket over the MC hole).
Add the beef mince and cook for 5 minutes, 100 degrees, REVERSE, Speed 1 (with the MC off but the splatter guard or rice basket over the MC hole).
Mix the cornflour, beef stock powder and water in a small bowl until dissolved. Add to the Thermomix bowl along with the tomato sauce, Worcestershire sauce, barbecue sauce and Vegemite. Cook for 10 minutes, 100 degrees, REVERSE, Speed 1 (with the MC off but the splatter guard or rice basket over the MC hole).
Cut 12 circles from the shortcrust pastry sheets to fit your pie maker (see recipe notes if cooking in the oven).
Place the shortcrust pastry circles into the base of the pie maker shells (you'll need to do this in batches - I did 3 X batches of 4 pies in my Kmart pie maker).
Spoon the beef mince filling over the top.
Cut 12 circles from the puff pastry sheets and place over the top.
Brush with the lightly beaten egg.
Cook for 10 minutes or until the pastry is golden brown.
Serve immediately or allow to cool and freeze in an airtight container for up to 3 months.