Cream the butter and sugar with an electric mixer until pale and light.
Add vanilla essence and mix well. Add the egg and mix thoroughly.
Sift together the flour, cocoa powder, baking powder, bi-carb and salt. Gradually add to the creamed mixture to form a dough. Wrap dough in cling film and refrigerate for an hour.
Preheat oven to 170oC. Line three oven trays with baking paper.
Lightly flour the work surface and roll out the dough evenly to a thickness of approximately 5mm. Using a bunny cookie cutter, cut out shapes from the dough and arrange on the prepared baking tray.
Bake for 10-12 minutes on the middle shelf.
Allow the biscuits to cool completely. Meanwhile, cut each marshmallow in half (easiest to use kitchen scissors). Melt chocolate and use to affix marshmallow on the bunny as its tail. Tie ribbon around the bunny's neck.