01 - 
                Preheat oven to 350°F and grease a half sheet pan (13x18 inches) with nonstick spray. Set aside.
              
              
              
                02 - 
                In a large mixing bowl, stir together the flour, sugar, and salt. Set aside.
              
              
              
                03 - 
                In a saucepan over medium heat, melt the butter. Whisk in cocoa powder until thoroughly combined. Stir in boiling water and increase heat to medium-high. Bring to a boil and let boil for 30 seconds before turning off heat.
              
              
              
                04 - 
                Pour the hot cocoa mixture over the flour mixture and stir to combine, scraping the bottom and sides well.
              
              
              
                05 - 
                In a medium bowl, whisk together buttermilk, eggs, baking soda, and vanilla extract. Stir the buttermilk mixture into the combined chocolate and flour mixture.
              
              
              
                06 - 
                Pour the batter into the prepared baking sheet. Bake for 15-20 minutes, or until the top springs back lightly and edges begin to pull away from the pan.
              
              
              
                07 - 
                While the cake bakes, prepare the frosting by melting the butter in a saucepan over low heat. Whisk in cocoa powder, then add milk, vanilla, and powdered sugar until smooth. Stir in chopped pecans.
              
              
              
                08 - 
                Pour the frosting over the warm cake and use an offset spatula to spread it evenly to the edges.
              
              
              
                09 - 
                Allow the cake to cool until the frosting sets. Slice and serve.