Spray a 9x13 inch pan with baking spray, line with parchment paper so it has handles on the side, or spray well with baking spray on top.
Place a medium saucepan over medium heat and add 1 cup butter, 1 cup water, and 1/2 cup cocoa powder. Stir for the butter to melt and to combine all the ingredients. Bring to a boil and remove from heat.
Stir in 1 cup of sugar and vanilla extract.
In another medium bowl combine 2 cups of flour, 1 cup granulated sugar, salt, and baking soda.
Add the flour mix to the mixture in the saucepan. Stir to combine.
Add sour cream and eggs and blend until fully combined with no lumps.
Pour the batter into the prepared pan and spread evenly with a spatula.
Bake for about 18-20 minutes, or until a toothpick inserted in the center comes out with no wet batter on it. Careful to NOT overbake.
Once done, let cool for 20 minutes before adding the frosting.
Place a medium saucepan over medium heat and add butter and cocoa. Stir together until it comes to a boil, then remove from the heat.
Add milk, vanilla, melted chocolate, and stir to combine.
Spread the frosting over the slightly cooled cake.
Garnish with chopped pecans.
Serve this with milk or topped with vanilla ice cream.