Preheat the oven to 180ºC, fan 160ºC, gas 4. Grease 2 x 22cm round cake tins and line with baking parchment.
Mix all the cake ingredients together in a mixing bowl and divide between the two tins.
Bake for 40-45 minutes until a skewer comes out clean, then remove from the oven. Leave to cool in the tins for 10 minutes, then transfer to a wire rack to cool completely.
Meanwhile, make the icing. Beat the butter in a bowl until soft. Add half the icing sugar and the vanilla extract and beat until smooth.
Add the remaining icing sugar and beat again until smooth and creamy. This will take about 7 minutes.
Once the cake is cool, spread the buttercream on to one half and sandwich the other cake base on top. Dust with icing sugar.