01 - 
                Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, allowing overhang on the sides for easy removal.
              
              
              
                02 - 
                In a medium saucepan, melt butter over medium heat. Stir in brown sugar and vanilla until smooth. Remove from heat and fold in crushed pretzels.
              
              
              
                03 - 
                Transfer the caramel-pretzel mixture to the prepared pan, spreading evenly. Press down firmly to create a compact layer. Bake for 10-12 minutes until golden and slightly bubbly.
              
              
              
                04 - 
                Sprinkle chocolate chips evenly over the hot base. Return to oven for 1-2 minutes or until chocolate is soft. Spread melted chocolate with a spatula to cover the base. Sprinkle with sea salt flakes, if using.
              
              
              
                05 - 
                Allow to cool completely in pan. Lift out using parchment overhang and transfer to a cutting board. Slice into bars.