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 170°C. 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 heart-shaped biscuit cutters, 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 before decorating.
To decorate, melt chocolate and carefully place into a zip-lock bag. Snip the smallest amount off the corner of the bag and drizzle the chocolate over the biscuits in a zig-zag fashion. Scatter over the sprinkles before the chocolate has set.