First make the shortbread-
- Preheat the oven to 160C/140C Fan/Gas 3 and line a baking tray with baking paper.
- Mix together the butter and sugar, either by hand or using an electric hand whisk, until pale and smooth. Gently mix in the flour until completely incorporated (try not to work the flour too much or the biscuits will not be so crumbly). Using your hands, squeeze the mixture together into a ball of dough.
- Gently roll the dough out to about 5mm/¼in thick (dust the work surface with a little flour if the dough sticks). Cut into small heart shapes using a biscuit cutter . Transfer the biscuits onto the baking tray and chill in the fridge for 15 minutes to rest.
- Sprinkle each biscuit with a pinch of sugar. Bake for 15–20 minutes, or until pale golden-brown.
- Transfer the biscuits to a wire rack to cool completely (try not to eat them!)
Next make the chocolate butter cream-
- Place the softened butter into a mixing bowl, add all the other ingredients and using a low speed on an electric whisk, beat together to form a chocolatey cream.
- Use the tip of a teaspoon or a little piping bag to pop the buttercream on 12 hearts, aim for the center. Sandwich with the other hearts and lightly dust with icing sugar.