01 - Preheat oven to 300°F. Line a large baking sheet with parchment paper.
02 - Place the mini pretzels in a large mixing bowl and set aside.
03 - In a saucepan over medium heat, melt the butter. Stir in the brown sugar, corn syrup, and sea salt. Bring to a gentle boil, stirring frequently, and simmer for 2 to 3 minutes until smooth and bubbling.
04 - Remove the saucepan from heat and stir in the vanilla extract until well combined.
05 - Quickly pour the hot toffee mixture over the pretzels. Use a spatula to gently toss until all pretzels are evenly coated.
06 - Spread the coated pretzels in a single layer on the prepared baking sheet.
07 - Bake for 12 to 15 minutes, gently stirring halfway through, until the toffee is set and bubbly.
08 - Remove from the oven and immediately sprinkle with flaky sea salt if desired.
09 - Allow pretzels to cool completely on the baking sheet. Once cooled, break apart any clusters and transfer to an airtight container.