Place the pastry sheets onto the bench and allow to defrost.
Meanwhile, heat the olive oil in a frying pan over medium-high heat.
Add the onion and cook until just starting to soften.
Add the cubed beef and cook until just browned (approx 5 minutes).
Add the beef stock, tomato paste and worcestershire sauce and stir.
Simmer uncovered for 45 minutes (or until starting to thicken), stirring occasionally.
Mix the cornflour and water together until completely dissolved.
Pour into the beef mixture and stir.
Allow to simmer and thicken (the mixture should be thick).
Season the mixture with salt and pepper and then set aside to cool completely (the mixture will continue to thicken on standing).
Preheat oven to 200 degrees celsius (fan-forced).
Light grease a 12 hole muffin tray.
Use a small bowl or cutter to cut 12 circles from the shortcrust pastry sheets.
Use your fingers to press them into the muffin tray holes (each pastry round should be large enough to slightly overhang).
Divide the mixture equally between the 12 muffin tray holes (being sure not to over-fill).
Cut 12 slightly smaller rounds from the puff pastry sheets.
Place them over the top of the meat pies and use your fingers to seal the overhanging shortcrust pastry to the puff pastry top.
Lightly brush over the beaten egg.
Sprinkle with sesame seeds.
Bake for 30 minutes or until golden.
Serve immediately or freeze in an airtight container for up to 3 months.