Grease 15x10x1 inch or 13x 9 x 2 inch baking pan. Preheat oven 350 degrees

Medium bowl mix stir flour, sugar, baking soda, salt. Set aside (kitchen aide mixer bowl)

Medium saucepan mix butter, cocoa powder and 1 c water. Bring mix to boil, stirring constantly. Remove from heat and add cocoa mix to flour mix and beat with electric mixer on high speed until thoroughly combined.

Add eggs, buttermilk, and vanilla. Beat for 1 min (thin batter). Pour batter into pan.

Bake at 350 for 25 min in 1 inch pan or 35 min in 2 inch pan or until toothpick comes out clean.

While baking, make frosting. In medium saucepan combine 1/4 c butter, 3 tbsp cocoa powder, and 3 tbsp buttermilk. Bring to boiling.

Remove from heat. Add 2 1/4 c sifted powder sugar and 1/2 tsp vanilla. Beat until smooth.

Pour warm frosting over warm cake and spread.