Cream butter, shortening, and brown sugar thoroughly. Blend in egg and molasses. Sift together the remaining ingredients. Stir into sugar mixture. Shape dough into 2 cm balls. Place 5 cm apart on greased baking sheets. Flatten each ball with the bottom of a glass that has been greased and dipped into sugar. Bake in preheated 180ºC . oven for dozen to 15 minutes. Cool cookies on racks and store in airtight tins. Makes 4 dozen cookies.