Combine the popcorn and nuts in a large oiled heatproof bowl.
Have ready an oiled baking sheet or jelly roll pan and a large wooden spatula coated in oil.
In a heavy saucepan combine the sugar, corn syrup, and water, and bring the mixture to a boil, stirring.
Simmer the mixture until the sugar is dissolved.
Add the butter and cook, stirring occasionally, until a candy thermometer registers 280° F.
Continue to cook, stirring constantly, until the temperature reaches 298°, then immediately pour the caramel syrup over the popcorn and stir to coat the mixture.
Pour out onto the baking sheet, flattening into an even layer, and let cool completely.
Break into bite size pieces and store in airtight containers.