Spray large shallow roasting pan with cooking spray. Add popcorn and nibs and place in preheated 250° F oven while preparing caramel.In heavy 2-quart saucepan, stir brown sugar, corn syrup, butter and salt. Stir constantly, bring to boil. Without stirring, boil 5 minutes. Remove from heat, stir in vanilla and baking soda (mixture will foam). Pour over warm corn and nibs and stir. Bake in 250° oven, stirring occasionally, for 1 hour. Remove from oven and spread on foil coated with cooking spray to cool. Break up with hands. Store in an airtight container.