Pop corn and place in a brown paper grocery sack. Combine brown sugar, butter, syrup and salt in 2 quart dish. Bring to boil in microwave. (In my microwave, it takes about 4 minutes on high. I also stir all the above together so it boils faster.) Once it comes to a boil, cook on full power for 2 minutes. Remove from microwave and stir in soda. Pour over popcorn in bag. Shake! Shake! Shake! and cook in bag on high in microwave for 1 1/2 minutes. Take out and Shake! again and cook another 1 1/2 minutes on high. Tear open the bag and dump out on wax paper to cool. Break apart and put in airtight container. Add nuts or other if desired before putting sauce over popcorn.