Preheat your oven to 350°F. Line two large baking trays with parchment paper.

Gently melt chocolate in the microwave or in a heatproof bowl set over a saucepan containing ½ inch of simmering water and let cool slightly.

In a large bowl, cream butter and brown sugar using a wide rubber spatula until light, creamy and smooth. It should look like damp sand and more like a paste than an aerated mixture. Mix in egg until well incorporated. Add melted chocolate, coffee and vanilla extract and stir in until combined. Sprinkle flour, baking soda and salt over the chocolate mixture and fold it in evenly.

Turn the soft dough onto a piece of plastic wrap and form it into a 12” log, using the plastic to help you roll it out without sticking. Wrap the log in the plastic and twist at the ends. Refrigerate for 15-20 minutes, until firm. It will firm up quickly as the chocolate sets. If it becomes too hard, let the log stand at room temperature for 15 minutes before slicing.

Slice the log into 24 ½-inch rounds and place on prepared baking tray, spacing them 2 inches apart. Bake for 8-10 minutes, until puffed, slightly cracked and dry looking but still moist in the middle. They will still feel soft when ready but will set as they cool. Transfer trays to a wire rack and let cookies cool for a couple of minutes on the baking tray before transferring to a wire rack to cool completely.