Preheat the oven to 350.
Add the pretzels and brown sugar to a food processor, process until the pretzels have turned to crumbs. While the processor is running add the butter in a slow stream. Allow to process until well combined.
Spray an 8X8 pan with cooking spray, add the crust to the bottom of the pan in an even layer. Using your hands or a heavy bottomed mug press the crust until well compacted.
Bake at 350 until lightly browned, about 12 minutes.
Remove from oven, allow to cool.
Add the chocolate, 1/3 cup stout, heavy cream and butter to the top of a double boiler over medium heat. Stir until all the chocolate has melted and is well combined, remove from heat, pour into an even layer on top of the crust.
Allow to chill in the fridge while you prepare the next layer.
Add the heavy cream, cocoa powder, powdered sugar and salt to the bowl of a stand mixer. Beat on high until soft to medium peaks form.
Slowly add the vanilla and beer, mixing until peaks return.
Add to the pan in an even layer, chill until set, at least two hours, and up to two days.