For the espresso kisses:

1. Place the chocolate in a heatproof bowl. Set aside.
2. Place the cream and espresso powder in a small saucepan set over low heat. Heat, stirring occasionally, until the mixture reaches a light rolling boil.
3. Pour the hot cream mixture all over the chocolate and let it stand for 1 minute to acclimatise.
4. Using a rubber spatula, gently stir the cream into the chocolate until it is melted and smooth.
5. Set the bowl aside to reach room temperature then chill in the fridge until firm but smooth enough to pipe, 15 to 20 minutes. Stir occasionally.
6. Spoon the chocolate mixture into a piping bag fitted with a 1 cm / ½ inch round nozzle. Pipe out 16 x 2 cm (3/4 inch) chocolate kiss drops onto a baking tray lined with parchment paper. Chill in the refrigerator until hard then decorate with gold leaf, if using.

For the cookies:

1. In the bowl of a stand mixer set on medium speed and fitted with the beater attachment, or with handheld electric beaters, beat the butter and sugars until light and fluffy, 4 minutes.
2. Increase the speed to medium-high and add in the egg yolks followed by the vanilla bean extract and liqueur, if using. Beat until well combined. Pause mixing to scrape down the bowl as needed.
3. In a separate medium sized bowl, whisk together the flour, baking soda, espresso and salt.
4. Set the mixer speed to low then add the dry ingredients to the beating butter mixture in two separate additions. Beat until just combined. Pause mixing to scrape down the bottom and sides of the bowl as needed.
5. Remove the bowl from the mixer and using a rubber spatula, fold through the chocolate.
6. Wrap the dough bowl in clingfilm and chill for at least 1 hour, preferably overnight.
7. When you are ready to bake, pre-heat the oven to 180 C (350 F). Line three baking trays with parchment paper and set aside. Remove the dough bowl from the refrigerator and let stand at room temperature for 30 minutes before using.
8. Use an ice-cream scoop to scoop out 16 even sized balls of dough, or use a generous tablespoon as a measure. Place the dough balls onto the baking trays, spaced well apart to allow for spreading.
9. Bake for 10 to 13 minutes or until golden, crisp on the outside but slightly soft in the centre. Make sure to rotate the sheets halfway through baking to prevent unevenly baked cookies.
10. Remove the cookies from the oven and immediately press a chocolate kiss drop onto the sides of each cookie.
11. Let the cookies harden on their trays for 8 minutes before transferring to a wire rack to cool slightly before serving.