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 on 100 degrees, 3 minutes, Speed 1.
Add the beef mince and cook on 100 degrees, REVERSE, 5 minutes, Speed 1.
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 on 100 degrees, REVERSE, 10 minutes, Speed 1.
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.
If you don't have a pie maker, you can cook these in the oven in muffin tins on 200 degrees celsius for 20 minutes or until golden.