Preheat the oven to 325°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving a little overhang on the sides.
Melt the butter in a medium saucepan over low heat. Remove it from the heat and stir in the sugar, cocoa powder, and salt until combined.
Let the mixture cool for about 5 minutes, then stir in the vanilla.
Add the eggs one at a time, mixing well after each addition. Continue stirring for about 30 seconds, until the batter looks smooth and glossy.
Add the flour and stir just until you no longer see dry streaks.
Pour half the brownie batter into the prepared pan and spread it out. Scatter 1/2 of the pretzels over the batter, then top with the remaining batter. Drizzle the caramel sauce over the whole top. Then use a knife to swirl the caramel into the brownie mix, for a marbled effect.
Sprinkle on the rest of the pretzels and the mini chocolate chips
Bake for 35-40 minutes. Remove when a toothpick comes out clean.
Let brownies cool completely in the pan for at least an hour. If they’re still gooey when you cut into them, refrigerate for 20-30 minutes to firm up. Then cut into squares.