So there's two good reasons to make this pie right now... it's rhubarb season and British Pie Week. It also happens to be a simple recipe that is hard to mess up. If you like it sweeter, you can increase the amount of sugar, but I enjoy the tartness of fresh rhubarb and Braeburn apples.
1 tsp ground cinnamon
135g brown sugar
2 sheets shortcrust pastry
Preheat oven to 180°C. Dice 200g apples and 200g rhubarb, and toss to coat evenly in 1 tsp ground cinnamon and 75g brown sugar. In a skillet on a hob, melt 70g butter with another 60g brown sugar. Remove from heat.
Lay a sheet of ready-made shortcrust pastry (a few inches wider in diameter than the skillet) over the melted butter. Fill with the apple and rhubarb mix, fold the edges of the pastry in, then cover with another sheet of pastry. Brush over with one beaten egg, cut a few slits to let air escape, and bake for 1 hour. Let cool before serving with custard.