Super rich, decadent chocolate sheet cake with a layer of pretzels baked into it, with a thick chocolate glaze, another layer of crispy, salty pretzels, and an optional drizzle of peanut butter.
Bring water to a boil in a small saucepan. While that comes to a boil, melt the butter in a medium saucepan over medium low heat. Whisk in the cocoa. Whisk the boiling water into the butter and cocoa mixture. Let it boil for 1 minute then remove from the heat and set aside to cool briefly.
In a large bowl, combine the flour, sugar and salt. Stir together and set aside. Pour the chocolate mixture in and whisk until there are no more dry pockets.
In another bowl, mix together the buttermilk, baking soda, vanilla and eggs until even, then pour into the flour and chocolate mixture and stir with a spoon until smooth.
Pour into an ungreased jelly roll pan (or rimmed baking sheet). Arrange the small pretzels in rows over the batter and then bake for 20 minutes.
While the cake is baking, make the icing:
Melt the butter in a medium saucepan over medium-low heat. Whisk in the cocoa powder until smooth. Whisk in the milk, vanilla and powdered sugar until smooth.
As soon as you remove the cake from the oven, pour the warm icing over the top, taking care to distribute it as evenly as possible as you pour it, since you'll want to avoid spreading it with a spatula as much as possible. When the icing is evenly distributed, arrange another layer of small pretzels in rows. Allow the cake to cool completely. If desired, gently warm the peanut butter in a microwave safe bowl or in a saucepan until thinner. Stir well and drizzle over the cake. Allow it to sit for 5 minutes.
Slice the cake into pieces as large as the pretzels on top and serve. Leftovers can be kept tightly wrapped at room temperature for 4 to 5 days.
Nutritional information is an estimate and provided to you as a courtesy. You should calculate the nutritional information with the actual ingredients used in your recipe using your preferred nutrition calculator.