Step 1

Preheat oven to 350°F and grease a 9X13-inch pan.

Step 2

Cut butter into pieces and combine the 1 cup butter, 1/3 cup cocoa, and 1 cup water in a small saucepan and heat over low heat. Stir constantly until butter is melted.

Step 3

Remove the mixture from the heat. Using an electric hand or stand mixer, beat buttermilk, eggs, baking soda, and vanilla extract until smooth.

Step 4

Gradually add melted butter mixture, beating until mixed.

Step 5

In a medium bowl, combine sugar, flour, and salt. Add to buttermilk mixture and beat until blended. Pour batter into prepared pan.

Step 6

Bake for 30 to 35 minutes, or until set in the middle.

Step 7

Combine butter, cocoa, and buttermilk in a medium saucepan. Heat over medium heat, stirring constantly, until mixture is smooth. Remove from heat and stir in powdered sugar, vanilla, and pecans (if adding).

Step 8

Pour the frosting over cake while the cake is still warm. Allow the frosting to cool and set a bit before slicing.