Beat together the butter and sugar in a bowl until pale and fluffy. Add the remaining ingredients and mix until evenly combined.
Using 2 forks, place small heaps of the mixture, spaced slightly apart, on 2 greased baking sheets. Sprinkle with extra demerara sugar.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 15–20 minutes or until deep golden. Transfer to a wire rack to cool. Serve on the same day.