Preheat the oven to 190°C (170° fan) and line a 12-hole cupcake tin with paper cases.
Combine the flour, sugar, butter, eggs and vanilla extract in a bowl. Whisk with an electric whisk for 2 minutes or until smooth. Fold in the chopped mini eggs.
Divide the mixture between the cake cases then transfer the tin to the oven and bake for 15 minutes or until a skewer inserted in the centre of a cake comes out clean. Transfer the cakes to a wire rack and leave to cool completely.
To make the buttercream, beat the butter until smooth then beat in the icing sugar and vanilla extract. Spread the buttercream on to the cakes.
Cut the marshmallows in half and dip the cut side of each one in demerara sugar. Arrange two halves on top of each cake to look like bunny ears.
Serves 12 cupcakes