Step 1: Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the sides. Set aside.
Step 2: In a medium bowl, combine the crushed pretzels and melted butter. Mix until the pretzels are evenly coated.
Step 3: Press the pretzel mixture firmly into the bottom of the prepared pan. Use the back of a spoon or a flat-bottomed glass to create an even, compact layer.
Step 4: Place the pan in the refrigerator for at least 15 minutes to chill and set the crust.
Step 5: While the crust chills, combine the unwrapped caramels and heavy cream in a microwave-safe bowl. Microwave on high for 1-2 minutes, stirring every 30 seconds, until the caramels are melted and smooth. Alternatively, melt over low heat on the stovetop.
Step 6: Pour the warm caramel mixture evenly over the chilled pretzel crust. Return the pan to the refrigerator for another 30 minutes to allow the caramel to set slightly.
Step 7: In a separate microwave-safe bowl, combine the chocolate chips and vegetable oil (if using). Microwave on high for 1 minute, then stir. Continue microwaving in 30-second intervals, stirring until the chocolate is completely melted and smooth.
Step 8: Pour the melted chocolate evenly over the caramel layer. Gently spread it to cover the entire surface. If desired, sprinkle with flaky sea salt immediately.
Step 9: Return the pan to the refrigerator for at least 1.5 to 2 hours, or until the chocolate layer is completely set.
Step 10: Once set, use the parchment paper overhang to lift the entire slab out of the pan. Place it on a cutting board and slice into 16 bars using a sharp, warm knife. Enjoy!