Preheat the oven to 250° and line a large-rimmed baking sheet with aluminum foil.
In a large, heavy bottom saucepan over medium heat, combine the brown sugar, corn syrup and butter, stirring constantly, until it starts to lightly bubble.
Keep it consistent at a low boil for 5 minutes, without stirring. Remove from the heat and stir in the baking soda and vanilla.
Spread the popcorn onto the prepared baking sheet and pour the syrup over top, tossing gently to coat.
Bake for 35 minutes. Remove and sprinkle the top with bacon, returning to the oven and cooking for another 5 minutes.
Remove and allow to cool fully.
After cool, sprinkle with mini chocolate chips and fleur de sel, if desired.
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Notes
This is best enjoyed the same day as making, but it can be stored in a paper bag or airtight container for up to a week.