Using an electric mixer, cream together butter and sugar until light and fluffy. Add an egg, vanilla extract and coffee extract, combine together. In a separate bowl sift together the flour, cocoa powder and salt, and mix to combine. Add dry ingredients into the butter mix and fold until the ingredients are combined.

Line the baking tray with baking paper. Roll balls of dough, about 1 tablespoon each, and place on a baking tray leaving 3-4 cm space between each cookie. Using your thumb (or a back of measuring teaspoon), make an indent into each cookie. Once you have used up all of the dough, place cookies in the fridge for 30-40 minutes.

Heat the oven to 180°C (165°C fan). Remove cookies from the fridge and place in the middle shelf in the oven. Bake for 10 minutes, rotating the baking tray half way through. If the indents lost their shape, use the back of the spoon to gently press in the middle of each cookie and make the indents again. Allow the cookies to cool for about 10 minutes and transfer to a wire rack.

Place the chopped chocolate into a medium bowl. Pour the cream into a small saucepan over medium heat and bring it to the gentle boil. Once the bubbles start to appear on the surface, remove the cream from the heat and pour over the chopped chocolate. Stir them both together vigorously, until you have smooth, shiny ganache and all the chocolate has melted.

Spoon the ganache into each cookie, or transfer it into a piping bag with a nozzle and pipe small amounts of ganache into each cookie. Add some festive sprinkles on top.