Heat half the oil in a medium non-stick saucepan over medium-low heat.
Add onion, carrot and celery, cook for 15 minutes or until onion is soft. Increase heat to medium-high, cook for 5 minutes, stirring occasionally until vegetables are golden. Remove vegetables from pan and set aside.
Place the flour, mustard, salt and pepper together in a large mixing bowl, stirring until well combined. Toss the beef in the seasoned flour until well coated.
Add remaining oil to the pan and place over a medium-high heat. Brown the beef in batches, to prevent it from stewing. Return the browned beef and vegetables to the pan, add the garlic and cook for 1 minute.
Pour over the Guinness and beef stock, stirring to combine and bring to the boil. Reduce the heat, cover and simmer for 50 minutes. Remove the lid and cook for a further 10 minutes. Remove pan from heat, add the stilton, thyme and sage, stirring until the cheese has melted, allow mixture to cool.
Preheat oven to 200°C (180°C fan-forced).
Roll the sour cream shortcrust pastry to a thickness of 3mm and cut 6 x 16cm rounds to line the bottom of the pie tins. Evenly divide the cooled beef mixture between the six pie cases. Brush the edges with the egg glaze.
For the pie tops, roll the all butter puff pastry to a thickness of 2.5mm and cut 6 x 13cm rounds. Cover each pie with a pastry round, pressing the edges with a fork to seal. Cut an air hole in the top of each pie and brush pie tops with egg glaze.
Place pies on a baking tray, bake in preheated oven for 45 minutes or until pastry is cooked and golden.