Ingredients:For the cake:250g unsalted butter, at room temperature
250g caster sugar
3 eggs, beaten
2 teaspoons vanilla extract
320g sultanas
375g plain flour
1.5 teaspoons baking powder
170ml buttermilk

For the custard buttercream:
150ml whole or semi-skimmed milk
125g caster sugar
2 egg yolks
175g unsalted butter, at room temperature
2 teaspoons vanilla extract

How to make:
- Preheat the oven to 160°C/fan oven 140°C/315°F/Gas mark 2-3.