Place the Puff Corn in a large roasting pan.
In a 2-quart saucepan, cook together the butter, brown sugar, and light corn syrup for 2 minutes.
Add the baking soda to the mixture. (This will cause the mixture to foam, so a 2-quart saucepan is necessary.)
Pour the caramel mixture over the Puff Corn and stir until well mixed.
Bake at 250 degrees for 45 minutes, stirring at least every 10–15 minutes.
Remove from the oven and pour onto wax paper.
Cool completely, then break apart.