Caramel Popcorn

Preheat oven to 300 degrees F. Spread popcorn and nuts, if using, on a baking sheet with sides and set aside.

Combine sugar, corn syrup, butter and salt in a heavy medium saucepan; bring to a boil over medium-low heat, stirring occasionally to dissolve the sugar. Clip a candy thermometer to the pan and cook until the mixture reaches 250 degrees F and is at hard-ball stage (when a bit of syrup dropped into ice water forms a hard ball), 2 to 3 minutes. Remove pan from the heat and immediately stir in baking soda. Pour the mixture over the reserved popcorn and nuts, stirring until most of the kernels are coated.

Bake the popcorn for 15 minutes. Stir, coating any kernels that were not coated at the beginning. Continue baking until amber, 5 to 10 minutes longer. (Longer baking produces a deeper caramel color and flavor.) Let cool until the caramel has almost hardened, about 2 minutes. Gently break up large clumps and let cool completely.