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.