In a large mixing bowl, whisk together flour, sugar, and salt. In a medium size saucepan over medium high heat, melt butter and then add the cocoa. Whisk to combine.
Add boiling water to the saucepan and allow the mixture to boil for 30 seconds, then remove from the heat. Pour the chocolate mixture over the flour mixture, and stir to combine.
In a small bowl, whisk together the buttermilk, beaten eggs, vanilla and baking soda. Stir this mixture into the first mixture. Pour into your sheet cake pan (or the pan of your preference) and bake for 20 minutes.
To Make the Frosting
While the cake is baking, make the icing. Melt butter in a saucepan over medium high heat. Add cocoa and whisk to combine, then remove from heat. Add the milk, vanilla, and powdered sugar. Whisk to combine. Add the pecans, if desired and stir to combine. Pour the frosting over the warm cake. Enjoy!