Place freshly popped popcorn in a big ol' pan or bowl. I use an enamel dish pan. You need lots of stirring room in the pan. Don't crowd yourself or the popcorn.
Place sugar, syrup, butter and salt in a heavy 2 quart saucepan. Bring to boil over medium heat, stirring constantly.
Bring the mixture comes to a full boil. Boil an additional 2 minutes and stir constantly.
Remove from heat and stir in vanilla and baking soda.
Slowly pour hot mixture over popcorn stirring constantly as you pour. This is easier with a helper. One pours slowly while one stirs constantly. Pouring slowly and stirring constantly by yourself gets a tricky. Try patting your head and rubbing your belly at the same time. I was by myself when I made this. I kept pouring constantly and stirring slowly.
Stir until popcorn is well coated.
Since the mixture is still warm, I find it easier to scoop out cupfuls rather than try to form the balls by hand. Spray a 1-cup measuring cup with a non-stick spray. Scoop out a tightly packed cupful onto waxed paper to dry and cool. Repeat with remaining popcorn mixture.
As soon as the mixture has cooled completely, wrap individually in plastic wrap and tie with a cute little string