Prepare the Baking Sheet: Preheat the oven to 200°F. Line a large baking sheet with parchment paper. If necessary, use two baking sheets so the pretzels aren't overcrowded. Place the pretzels in a large mixing bowl.
Make the Toffee: Melt the butter in a heavy-bottomed saucepan over medium heat. Add the brown sugar and corn syrup, stirring constantly until the mixture is fully combined and bubbling. Continue cooking for 3 to 4 minutes, stirring constantly to prevent the toffee from burning. Remove the saucepan from the heat and immediately stir in the baking soda, salt, and vanilla extract. The mixture will bubble up when the baking soda is added, so be careful.
Coat the Pretzels: Pour the hot toffee mixture over the pretzels. Quickly stir until the pretzels are evenly coated. Work quickly during this step because the toffee begins to set as it cools.
Bake Until Crisp: Spread the coated pretzels in an even layer on the prepared baking sheet. Bake at 200°F for 1 hour, stirring every 15 minutes to help distribute the toffee and ensure an even coating.
Cool Things Down: Remove the pretzels from the oven and let them cool completely on the baking sheet, about 20 minutes.
Break into Pieces: Once completely cool, break apart any large clusters. Sprinkle with English toffee pieces or a little sea salt, if desired. Serve at room temperature for the best crunchy texture.
Notes
This recipe makes 6 cups, or 16 servings. Use small pretzels for even coating.
Stir constantly when making toffee to prevent burning.
Do not skip lining with parchment to prevent sticking.
Cool completely before storing to maintain crispiness.
Optional sea salt enhances the sweet-salty flavor.
Use a heavy-bottomed pan for even heat distribution.
Add a drizzle of melted chocolate for extra indulgence.
Work quickly when coating pretzels, as toffee sets fast.