Preheat your oven to 180°c (160°c for fan assisted ovens or Gas Mark 4) and line a 12-hole muffin tray with paper cases.
In a large bowl, cream the butter and sugar until light & fluffy.
Add the eggs to the mixture one at a time, ensuring the first is well combined before adding the second. Once both eggs are combined, add the vanilla extract.
Sift the flour to the mixture and fold in gently until you have a smooth batter.
Spoon the batter evenly between your cases. Bake for around 15 minutes in your pre-heated oven, or until a skewer inserted comes out clean.
Once cool enough to touch, move your fairy cakes to a wire rack to cool whilst you prepare your buttercream.