Preheat the oven to 350 degrees. Spray a 13x9-inch dish with cooking spray, then line it with parchment paper.
Sift the flour, sugar, baking soda, and kosher salt in a larger mixing bowl. Set aside.
Whisk the buttermilk, eggs, and vanilla extract in a bowl until combined. Set aside.
In a saucepan, whisk the butter, cocoa powder, and brewed coffee until everything is incorporated and smooth.
Slowly pour the chocolate/coffee mixture into the flour as you whisk.
Once incorporated, do the same for the buttermilk mixture. Whisk until the cake batter is evenly combined.
Pour the cake batter in the prepared pan. Bake in the oven for 25 minutes, or until a toothpick comes out clean. Set the pan on a rack to cool completely.
To make the frosting, whisk together the butter, cocoa powder, whole milk, vanilla extract, and kosher salt over medium-low heat. Once the butter is melted, gradually add in the powdered sugar, whisking constantly.
When all of the sugar is incorporated and the frosting is smooth, turn off the burner and fold in the chopped pecans.
Pour the frosting over the cooled cake and spread evenly. Sprinkle more chopped pecans on top. Let the cake and frosting cool before slicing and serving.
