Preheat the oven to 180°C, fan 160°C, gas 4, and line a 12-hole muffin tin with paper cupcake or muffin cases.
Put the butter, caster sugar, eggs and vanilla extract into the bowl of a free-standing electric mixer (or you can use a handheld electric whisk and mixing bowl). Then sift in the flour and beat for 1–2 minutes until light and creamy. Divide the mixture evenly between the paper cases.
Bake in the preheated oven for 20–25 minutes or until well risen and a skewer inserted into one of the cakes comes out clean. Remove from the oven and leave to cool in the tin for 10 minutes. Transfer to a wire rack to cool completely.
Meanwhile, make the chocolate buttercream. Beat the butter until soft and creamy. Sift the icing sugar and cocoa powder, and add to the creamed butter in two additions, mixing on a low speed, incorporating the milk, and beat for 3–5 minutes on a higher speed.
Dust your work surface and roll out a small amount of the fondant icing to a thickness of 5mm. Cut out 12 small bunnies using the bunny-shaped cutter. Colour a tiny piece of white fondant icing with a little pink food colouring and, using your hands, roll 12 tiny bunny tails. Leave to one side to dry.
Spoon the chocolate buttercream into a piping bag fitted with a star nozzle and swirl it on top of the cooled cupcakes. Top with three micro eggs and a fondant bunny to finish.