Step 1

Grease a 10x15 baking pan (or spray with cooking spray) and preheat oven to 350 degrees. See notes below regarding other pan sizes.

Step 2

Combine flour, sugar, baking soda and salt in a large mixing bowl. Whisk to incorporate ingredients then set aside.

Step 3

Combine buttermilk, eggs and vanilla extract in a small bowl then mix well and set aside.

Step 4

Melt butter in a small saucepan then whisk in cocoa powder and water or black coffee until smooth. Stir and heat over medium-high heat until boiling. Remove from heat.

Step 5

Pour hot cocoa power mixture into bowl with flour mixture then stir to incorporate. Add buttermilk mixture then whisk all ingredients together for one minute.

Step 6

Pour batter into prepared pan then bake for 20 minutes or until toothpick inserted in the middle of the cake comes out clean. Remove from oven then prepare icing.

Step 7

Combine milk, butter and salt in a small saucepan then heat until simmering. Remove from heat then stir in vanilla extract.

Step 8

Meanwhile, sift together powdered sugar and cocoa into a large mixing bowl (the sifting is optional but it prevents lumps). Pour hot milk/butter mixture into bowl with powdered sugar and cocoa powder then stir until smooth.

Step 9

Pour icing over warm cake. Let cake rest for a few hours before serving to ensure the icing sets up some before cutting the cake.

Step 10

Once the cake is cool, cover then store at room temperature.