Once you have popped the popcorn, remove any unpopped kernels. Now place the popcorn in a buttered metal bowl and place in a 200 degree oven to keep warm.
Combine the brown sugar, butter, corn syrup and salt in a saucepan and bring to a boil, stirring occasionally. Once it begins to boil, stop stirring for 5 minutes, or until mixture reaches 255 degrees on a candy thermometer.
Remove from heat and add baking soda. The mixture will start to foam, so stir well until blended. Pour the hot mixture over the pop-corn and toss gently with well buttered forks to distribute evenly.
Spread onto 2 ungreased baking sheets and bake at 200 degrees for 1 hour, stirring every 15 minutes.
Remove the caramel corm from the oven and allow to cool completely. Once cool, break it into clusters, and store in a tightly covered container. vintageholidaycrafts.com