Preheat oven to 400°F

Using butter, grease an 11x16 or similar size sheet pan.

To a heavy bottom sauce pan add 1 cup of butter (2 sticks), the water and 4 tablespoons cocoa powder. Bring the mixture to a boil, stirring until smooth. As soon as it’s boiling and smooth, take off the heat. Let cool 5 minutes.

Pour the chocolate mixture into large mixing bowl.

In a separate bowl mix together the sugar, flour and salt. Gradually add the dry mixture in to chocolate, beating well until smooth.

To the mixing bowl add in 3 eggs, sour cream and baking soda. Mix on low until smooth, scraping the sides as necessary.

Pour the batter into the greased sheet pan and bake for 20 minutes.

While the cake is baking prepare the frosting. The cake should be frosted as soon as it is removed from the oven.

Add 1/2 cup of butter (1 stick) to the same saucepan as earlier. Melt the butter. When it’s melted, add in 4 tablespoons of cocoa powder and 6 tablespoons milk. Continue cooking; as soon as the mixture starts to bubble take it off the heat and whisk in the powdered sugar and vanilla extract. Continue whisking until the frosting is smooth.

Spread the frosting evenly over cake with an offset spatula as soon as it is removed from oven.

Let cool completely and slice into squares.