Preheat the oven to 180C/350F/gas mark 4 and line 3 baking sheets with greaseproof paper or silicone liners.

Whisk together the butter, tahini and sugars with an electric mixer until light and fluffy then whisk in the egg and vanilla extract.

In a separate bowl sift together the flour and bicarbonate of soda then stir it into the butter mixture until combined.

Scoop out small amounts of the dough (about a tablespoon) and roll into balls, place them well spaced apart on the baking trays as they spread in the oven. (the dough is quite soft but as it is oily it shouldn't stick to your hands).

Dip the tines of a fork into hot water and press the dough balls lightly with the back of the fork in a criss cross pattern to flatten them. Re-dip the fork after each dough ball to prevent it from sticking.

Bake for 12-15 minutes until golden brown, allow to cool on the tray for a couple of minutes then transfer to a wire rack to cool completely. I prefer to bake them one tray at a time and place the other trays in the fridge.

Once cold store in an airtight container.