Preheat your oven to 180ºC (160ºC fan-assisted) and line a cupcake tray with 12 paper cases.
Using a stand mixer or handheld whisk, cream together the unsalted butter and light brown sugar until the mixture becomes pale and fluffy.
Gradually add the eggs, one at a time, ensuring each is fully incorporated before adding the next. Mix in the vanilla extract for an added layer of flavor.
Sift together the self-raising flour and cocoa powder, then gently fold these dry ingredients into the wet mixture until smooth and evenly combined.
Evenly divide the cupcake batter between the prepared cases, filling each approximately two-thirds full.
Bake for 20–22 minutes, or until the cupcakes are springy to the touch and a skewer inserted into the center comes out clean. Allow the cupcakes to cool completely on a wire rack before decorating.