Place butter in a large, heatproof bowl. In a medium saucepan, heat brown sugar, molasses and spices just to boiling point. Add baking soda and stir in. Pour this mixture over the butter and stir until it melts.
Beat egg and mix in; add flour, a cup at a time, and blend thoroughly. Turn out onto a lightly floured board and knead 1-2 minutes. Wrap in waxed paper and chill until firm (about an hour).
Preheat oven to 325 degrees F (170 degrees C).
Roll out to approximately 1/8 inch thickness on a lightly floured board and cut into desired shapes. Place on greased baking sheets and bake for 8 – 10 minutes.
Remove from sheets and cool on racks; may be decorated with piped icing or whatever else you like!