2. In a heavy 3-quart saucepan, combine the butter, corn syrup and sugar. Bring to a boil and remove from heat. Stir in the baking soda and vanilla.
3. Pour the hot mixture over the popcorn and nuts. Fold the top of the bag down a few times to close it. Shake the bag to mix the contents.
4. Fold the top of the bag down until the bag is compact. Place the bag in the microwave, cook on high for 1 minute, remove the bag from the microwave and shake the bag well. Repeat this step 2 more times.
5. Pour the caramel popcorn onto a parchment lined cookie sheet and cool. Break the corn and nuts into pieces. Store in an airtight container.