Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang on the sides to make removing the bars easier later.

Arrange the mini pretzels in a single layer across the bottom of the pan. Try to cover as much surface area as possible. For any gaps, crush a few pretzels and sprinkle them in to ensure even coverage.

In a medium saucepan, melt the butter and brown sugar over medium heat. Stir continuously until the mixture begins to boil. Once boiling, let it cook undisturbed for 3-4 minutes until it thickens and turns caramel-like. Remove from heat and stir in the vanilla extract.

Pour the hot caramel evenly over the pretzel layer. Use a spatula to spread it out, ensuring all the pretzels are coated. Place the pan in the oven and bake for 10 minutes, or until the caramel is bubbling.

Remove the pan from the oven and immediately sprinkle the chocolate chips over the bubbling caramel layer. Let them sit for 2-3 minutes to allow the chocolate to melt. Then, use a spatula to spread the chocolate evenly over the caramel.

If desired, sprinkle flaky sea salt, sprinkles, or chopped nuts over the melted chocolate. Let the bars cool at room temperature, then transfer to the refrigerator for 1-2 hours to set completely.

Once fully set, lift the bars out of the pan using the parchment paper overhang. Cut into squares or rectangles and serve.