Sift together the dry ingredients. Put butter, sugar and treacle into a pan and melt slowly over a low heat. Remove from the heat and stir in the sifted dry ingredients. Work with fingertips until well blended. Roll the mixture into small balls and transfer to greased baking trays, allowing plenty of room between each for spreading. Press flat with a knife or the prongs of a fork. Bake in the centre of the oven, at 350°F, 180°C, gas mark 4 for 10-15 minutes. Cool on a wire tray, then store in an airtight container.