Cream the butter and brown sugar together until soft and fluffy.
Beat in egg, salt and molasses until thoroughly mixed, be sure to scrape the sides of the bowl to ensure even mixing.
Sift dry ingredients together in a separate bowl.
Gradually mix the dry ingredients into the batter until well-blended.
Chill for at least two hours (overnight is best).
Preheat oven to 350°F or 180°C
Roll dough into walnut sized balls (3/4" - 2cm) and place on a greased cookie sheet.
Flatten slightly with the base of a glass dipped in white sugar.
Bake for 12 to 15 minutes.