Pop popcorn according to package directions, and pour both bags into the large brown paper bag. In Tupperwave® Stack Cooker 1¾-Qt./1.75 L Casserole, microwave butter, brown sugar and corn syrup on high power 3–5 minutes until melted, stirring halfway through to combine. Stir baking soda into caramel mixture. Foaming is normal. Pour caramel mixture over popcorn and shake to coat popcorn. Place bag in microwave and heat on high power 1 minute, shake. If popcorn still isn’t evenly coated, return to microwave and heat 1 more minute on high power and shake again Allow to cool before enjoying.