Melt margarine and sugar, then remove from heat. Combine dry ingredients in a large bowl, add eggs beaten with buttermilk. Add melted butter and sugar and mix well. Divide between three 9x13 pans and bake at 350 F for 45 minutes to an hour. Slice into rusk sized portions and place slightly separated on baking sheets. Place in oven at lowest oven temperature for about 12 hours, or till dry. Store airtight. (1 c self-rising flour = 1 c flour + 1 t baking powder + pinch of salt.)