Apple crumble cupcakes

Method

1. Heat the oven to 160°C fan/gas 4. To make the crumble mixture, put all the ingredients in a bowl and use your fingers to rub everything together until you get a clumpy, sandy mixture. Scatter over a small baking dish.
2. In a large mixing bowl, beat the butter and both sugars together until pale and creamy. Beat in the eggs, then fold in the flour and cinnamon with a pinch of salt. Fold through the chopped apple.
3. Line your cupcake tin with cases then spoon the batter into them. Bake in the oven for 20-25 minutes until a skewer inserted into the centre comes out clean. At the same time you put the cupcakes in the oven, add the crumble mixture too and bake for 10 minutes, then leave to cool.
4. While you wait, make the buttercream by beating the butter, icing sugar, custard powder (if using) and vanilla paste until smooth. Add the milk to loosen.
5. Once the cupcakes are cool, pipe or spoon the buttercream over the top, creating a little well in the centre. Sprinkle the crumble into the well.