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Heat 1 tbsp of the oil in a large frying pan over a medium heat. Fry the meat in batches until browned. Tip into a large bowl and set aside.
Heat the remaining oil in the same pan, then add the onions, carrot, celery and garlic. Fry for 8-10 mins until softened. Add this to the meat.
Simmer the wine in the pan for 10 mins to reduce. Tip in the meat and veg, then the spices, thyme, bay and stock. Cook for 30 mins, uncovered. Stir in the oats and simmer for 15 mins. Discard the bay, then season. Cool completely.
Heat the oven to 200C/180C fan/gas 6. Line a 20cm loose-bottom tin with the shortcrust pastry, pushing it into the sides of the tin. Leave 2cm of pastry overhanging and trim away the excess. Prick the bottom with a fork, cover with baking parchment and fill with baking beans. Bake for 15 mins. Remove the parchment and beans, and bake for another 15 mins until golden.
Trim the edges with a serrated knife and pack in the meat filling. Brush some of the egg around the edge of the pastry, then drape the puff pastry over the top, trim the edges and crimp all the way round with a fork. Use the puff pastry offcuts to make decorations for the pie, if you like (or see tip, below). Brush with more egg and make 4-5 holes in the top. Can be frozen for up to six weeks at this stage. Defrost thoroughly before baking. Bake at 190C/170C fan/gas 5 for 40-50 mins. Leave to rest for 10 mins before serving.