Divide popcorn and nuts between 2 ungreased rectangular pans, 13x9x2 inches. Cook brown sugar, margarine, corn syrup and salt over medium heat, stirring occasionally, until bubbly around edges. Continue cooking 5 minutes; remove from heat. Stir in baking soda until foamy. Pour over popcorn and nuts, stirring until corn is well coated. Bake uncovered in 200 degree F oven, stirring every 15 minutes, 1 hour. 300 calories per serving. Caramel Corn: Increase popped popcorn to 15 cups; omit nuts. *