1. Preheat oven to 350 degrees F.
2. Spray an 18x13 sheet cake pan with nonstick cooking spray.
3. In a large mixing bowl, combine flour, sugar, and salt.
4. In a medium saucepan over low heat, melt butter.
5. Once the butter is melted, whisk in cocoa powder until thoroughly combined.
6. Add boiling water and turn up the heat to medium.
7. Allow mixture to boil for 30 seconds and immediately turn off the heat.
8. Pour the cocoa/butter mixture over flour mixture, and stir lightly to cool.
9. Turn up the heat to medium. Allow mixture to boil for 30 seconds and immediately turn off the heat.
10. In a medium bowl, whisk together the buttermilk, eggs, baking soda, and vanilla.
11. Stir buttermilk mixture into chocolate mixture and mix well.
12. Pour into a baking tray and bake for 20 minutes.

Frosting

1. While cake is baking, make the frosting.
2. In a medium saucepan over low heat, melt butter. Once the butter is melted, whisk in cocoa powder until thoroughly combined.
3. Add milk, vanilla, and powdered sugar whisking until all ingredients are fully incorporated.
4. Pour over warm cake using an spatula to spread the frosting all over the cake.
5. Serve and enjoy!