Prepare your base. Preheat your oven to 350°F and line a baking sheet (approximately 10×15 inches) with parchment paper. Arrange the pretzels in an even layer, making sure they’re touching and creating a solid base.
Make the caramel mixture. In a medium heavy-bottomed saucepan, melt the butter over medium heat. Once melted, add the brown sugar and stir constantly until the mixture comes to a gentle boil (about 3-4 minutes). Lower the heat slightly and continue boiling for exactly 3 minutes without stirring.
Add flavor and pour. Remove the caramel from heat and carefully stir in the vanilla extract (it may bubble up, so be cautious). Immediately pour the hot caramel evenly over the pretzels, trying to cover as much area as possible.
Bake briefly. Place the pretzel-caramel mixture in the oven and bake for 5 minutes. This helps the caramel to further melt and coat all the pretzels evenly.
Add chocolate. Remove the baking sheet from the oven and immediately sprinkle the chocolate chips evenly over the hot caramel. Let sit for 2-3 minutes to allow the chocolate to melt, then use a spatula to gently spread the chocolate into an even layer.
Add toppings. While the chocolate is still warm, sprinkle the sea salt evenly across the surface. If using nuts, scatter them over the top as well, gently pressing them into the chocolate.
Cool and break. Allow the bark to cool completely at room temperature (about 30 minutes), then refrigerate for another 15-20 minutes to set the chocolate firmly. Once set, break or cut the bark into irregular pieces.