01 - Preheat oven to 350°F. Grease and line a 9x13-inch sheet pan with parchment paper.
02 - In a large mixing bowl, whisk together flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt until thoroughly combined.
03 - Add buttermilk, vegetable oil, eggs, and vanilla extract to the dry mixture. Mix until the batter is smooth and cohesive.
04 - Gradually pour in hot water while mixing until just combined. The batter will be thin.
05 - Pour cake batter into the prepared sheet pan and smooth the surface evenly with a spatula.
06 - In a medium bowl, combine crushed mini salted pretzels, melted unsalted butter, and brown sugar. Stir until the mixture is evenly coated.
07 - Distribute the pretzel crunch mixture evenly over the cake batter. Bake for 28 to 32 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.
08 - Heat heavy cream in a small saucepan until just beginning to simmer. Pour hot cream over semi-sweet chocolate chips, let sit for 2 minutes, then stir until glossy and smooth.
09 - Spread chocolate ganache smoothly over the cooled cake. Let ganache set at room temperature for 30 minutes.
10 - Dip half of each mini pretzel in melted semi-sweet chocolate and arrange on parchment paper to set.
11 - Once the ganache is set, arrange the chocolate-dipped pretzels on top of the cake. Slice and serve.