Preheat your oven to 180°c (160°c for fan assisted ovens or Gas Mark 4) and line a couple of baking sheets with grease-proof paper.
In a mug dissolve your coffee with the boiling water, stir well and set aside to cool.
In a large bowl, mix the flour and sugar before rubbing in the butter/margarine with your fingers, until you get a sandy consistency.
Add the egg to the cooled coffee and beat with a fork. Add to the bowl and bring the ingredients together to create a soft sticky dough.
Roll about a teaspoon of the dough into a ball and place on your pre-lined baking sheets. Repeat with the rest of the dough to make about 30 balls, leaving some space between each as they will spread a little while baking.
Bake in your pre-heated oven for 15-20 minutes until the balls resemble small biscuits and are dry-looking on top. Leave to cool on the baking sheets for a short while before transferring to a wire rack to cool completely.