Sift together flour, baking soda, and baking powder in a large bowl; set aside. Put butter and brown sugar into an electric mixer fitted with the paddle attachment; mix on medium speed until fluffy. Mix in spices and salt, then egg and molasses. Reduce speed to low. Add flour mixture; mix until just combined. Divide dough in half, and shape each half into a disk. Wrap in plastic wrap, and refrigerate until firm, at least 1 hour.