Pre-heat oven to 400 °F (200 °C). Lightly grease 2 x 12 hole muffin pans.
Heat oil in a large saucepan on high. Sauté bacon and onion for 3-4 minutes until onion is tender and transparent.
Add mince and brown for 4-5 minutes, breaking up the lumps with the back of a spoon as it browns. Blend in flour and cook, stirring for 1 minute.
Gradually stir in the Guinness, stock, tomato paste and rosemary and bring to the boil, stirring. Reduce heat and simmer uncovered for 10 minutes or until mixture reduces and thickens.
Transfer to a large bowl. Cool for 10 minutes and then chill in the fridge until cold (overnight is best).
Using a 12cm cutter cut 24 rounds from the short-crust pastry sheets. Ease each pastry round into each muffin hole. Using an 8cm cutter cut 24 rounds from the puff pastry. Spoon 2 tablespoons chilled filling into each pastry hole and brush edges with a little egg.
Top each pie with puff pastry rounds gently pressing together to seal. Brush with a little egg and sprinkle every second pie with sesame seeds and insert a small rosemary sprig into the others.
Using a sharp knife, make 2 small slits in top of each pie to form a steam vent. Bake for 20-25 minutes or until golden and puffed. Rest in pan for 5 minutes before serving.
There are 306 calories in 1 serving of Mini Beef & Guinness Pie.