Preheat the oven to 160°C. Season the beef with salt and pepper and toss with 2 tbsp flour until evenly coated.
Heat the oil in a large ovenproof heavy-based pan over high heat.
Add beef in batches and cook for about 5 minutes per batch, until well browned, then remove. Add more oil if pan dries out.
Add the onion with a pinch of salt and cook over low heat for about 5 minutes, until softened.
Add the tomato paste and 1 tbsp flour and cook out for a minute or so. Add the red wine and stock, and stir until the mixture boils.
Return the beef to the pan, cover the pan with foil, place in the oven and cook for 2 hours, or until tender, then stir through the peas and mint. Allow to cool, then chill in the fridge until cold (warm filling will ruin the pastry).
When the beef filling is ready, heat the oven to 180°C.
Divide the pie filling among four 300ml ramekins or pie dishes. Top each with a piece of pastry large enough to hang over the edge of each dish (it is important to remove the pastry from the freezer only 5-10 minutes before you need it, so it thaws but stays chilled). Press the pastry down firmly around the edges of the dishes and brush evenly with the egg yolk. Bake in the middle of the oven for about 40 minutes, until puffed and golden.
Serve warm with extra peas.