Toast almonds and pecans in dry frying pan or in oven. (If using the oven, place nuts on cookie sheet and toast for about 10-15 minutes in a 350-degree oven. If using the pan method, toast nuts on medium heat until lightly browned and crunchy.)
Spread popcorn and toasted nuts on a lightly greased baking sheet. Remove all un-popped kernels.
In a medium saucepan, combine sugar, butter and corn syrup. Cook on medium high heat until sugar dissolves and mixture comes to a boil.
Insert candy thermometer and stir occasionally, until thermometer reaches 290 degrees or soft crack stage. (Mixture will have a light caramel color.) Remove from heat and stir in vanilla.
Immediately drizzle hot mixture over popcorn and nuts, trying to cover as many kernels as possible. Quickly toss to coat with syrup. Important Note: Syrup will harden quickly, and may not cover all kernels. So return the baking sheet with popcorn mixture to a 350-degree oven. Every five minutes or so, toss the popcorn mixture with spatula until all kernels are covered. (It may take 2-3 times to completely coat each kernel without leaving pools of sugar mixture on baking sheet.)
Cool mixture. Break into chunks and store in a tightly covered container.