Preheat the oven to 350F. Line a 9x13in baking pan with parchment paper.
For the pretzel layer: mix together the pretzels, flour, brown sugar, baking soda and melted butter. Press firmly in the baking pan to form the bottom layer. Bake for 10 mins then remove from the oven. Melt the caramels in the microwave, stirring at 30 second intervals until melted. Pour over the pretzel crust.
For the brownie layer, mix the butter and cocoa powder together. In a separate bowl, whisk together the eggs, sugar and vanilla then pour in the butter. Add the flour, baking powder and salt and stir until just combined, being careful not to overmix. Pour over the pretzel crust and bake for 45 mins.