Blend the ingredients in a food processor until smooth. Grease a brownie baking tray, square or rectangular, with a little oil and cut a sheet of baking paper the size of the bottom. Grease thoroughly. Press the mixture into the tray. Bake the biscuit for 20 minutes in an oven preheated to 175°C (340°F/Gas 4). Leave to cool and transfer to a board. Leave to fully cool then cut into small cubes using a large knife. Keep in the refrigerator or freezer.