Step 1: Preheat your oven to 300°F (150°C). Line a large baking sheet with parchment paper or a silicone baking mat.
Step 2: Spread the mini pretzels evenly in a single layer on your prepared baking sheet.
Step 3: In a medium saucepan, combine the unsalted butter and packed light brown sugar. Place the saucepan over medium heat and stir continuously until the butter has melted and the sugar has dissolved.
Step 4: Once the mixture is simmering, continue to boil for exactly 3 minutes, stirring constantly. The mixture will darken slightly and thicken.
Step 5: Immediately and carefully pour the hot toffee mixture evenly over the pretzels on the baking sheet. Use a spatula to gently spread the toffee, trying to coat as many pretzels as possible.
Step 6: Transfer the baking sheet to your preheated oven. Bake for 5-7 minutes.
Step 7: Remove the baking sheet from the oven. Using a heat-resistant spatula or two spoons, gently stir and flip the pretzels to ensure they are thoroughly coated in the melted toffee.
Step 8: Return the baking sheet to the oven and bake for another 3-5 minutes, or until the toffee is bubbling vigorously and looks deeply golden brown. Watch carefully to prevent burning.
Step 9: Remove the pretzels from the oven. Immediately spread them out again on the parchment paper, ensuring they are in a single layer to prevent clumping. Allow them to cool completely on the baking sheet at room temperature for 30 minutes to an hour, or place in the refrigerator for 15-20 minutes to speed up hardening.
Step 10: Once completely cooled and hardened, break the large clusters of 3 Ingredient Butter Toffee Pretzels into smaller, bite-sized pieces. Store them in an airtight container at room temperature.