Have an instant-read thermometer ready or fit saucepan with a candy thermometer.
In a heavy-bottom four-quart saucepan, combine butter, sugar, and corn syrup. Over low heat, bring to a boil, stirring slowly. Continue to boil until the mixture reaches 290°F, 15-20 minutes. It will be a light amber color and smell like caramel and butterscotch.
1 cup salted butter, 1 cup white granulated sugar, 2 tbsp corn syrup
Remove from heat, add in the vanilla, and pour into the prepared baking sheet pan. Let cool for one minute and sprinkle with ¼ cup chopped nuts over the entire mixture. Sprinkle with chocolate chips. Let sit until melted, about two minutes. Spread the chocolate evenly with an offset spatula. Sprinkle with remaining chopped nuts. Let cool completely, about four hours.
1 cup chopped toasted pecans, 1 tsp vanilla extract, 6 oz dark chocolate chips
Once cooled completely, break into desired pieces. Store in an airtight container in a cool place for up to one month. If in a warm climate, store in the refrigerator.