Preheat oven to 375 degrees.
Line a large baking sheet with foil. Place bacon in a single layer on baking sheet. Place in oven and bake until crispy. Remove bacon from oven carefully and place bacon on paper-towel-lined platter. Allow to cool. Crumble bacon into small pieces. Reduce oven temperature to 200 degrees.
In a large saucepan, combine butter, brown sugar, salt and corn syrup. Place pan over medium heat. Allow caramel to boil for four minutes without stirring. Remove from heat and add baking soda.
Place popped popcorn in a large paper bag or large bowl with sealable lid. Sprinkle bacon on top of popcorn. Add nuts, if desired. Drizzle caramel sauce over popcorn. Shake to coat popcorn.
Line 2 large baking trays with parchment paper. Spoon popcorn onto each baking tray. Place in oven and bake for one hour, stirring every 15 minutes. Allow popcorn to cool on baking trays before breaking into small pieces and placing in a serving dish.
