Place the popcorn and toasted nuts in a very large mixing bowl and hold in warm area while preparing the caramel coating.
Melt the butter in a heavy duty sauce pot and stir in the sugar and corn syrup. Cook slowly, stirring often, until mixture reaches a rich brown color. Remove from the heat and whisk in vanilla extract. Be careful, caramel is hot and sticks to the skin if spilled.
Drizzle one half of the caramel over the popcorn mixture and gently toss, mixing well. Add the remaining caramel, and mix again.
Pour popcorn onto a wax-lined cookie sheet and cool completely. Gently break up the popcorn before serving.