Cream the margarine and brown sugar. Add flour gradually. Set aside one cup of this mixture for later use. To remainder, mix in baking soda and spices. Add eggs and combine very well. Stir in buttermilk. Pour into an ungreased 12x8 inch pan. Sprinkle the reserved mixture evenly over top then top with the chopped pecans. Bake for 30-40 minutes at 350 degrees. SAUCE: heat sugar and milk to the boiling point. Beat in margarine with a mixer then add rum. Cook until slightly thickened. Top squares of the gingerbread with this delicious sauce. Recipe by: Jo Merrill Posted to MC-Recipe Digest V1 #575 by Nancy Berry on Apr 17, 1997