This easy cake takes less than 45 minutes from start to finish and it's CRAZY delicious. The perfect chocolate cake for a picnic or potluck.
Preheat the oven to 350 degrees. Grease a half-sheet baking pan (18 in × 13 in x 1 in).
In a saucepan over medium heat, melt the butter, cocoa powder and water together, stirring until smooth.
While that cooks, whisk together flour, sugar, baking soda, and salt in a mixing bowl. When the butter/cocoa/water mixture is smooth, stir it in and mix well.
Add the eggs, sour cream and vanilla and stir until very well combined.
Pour the batter into the prepared pan and bake for 20 minutes.
While the cake bakes, make the frosting by melting the butter, cocoa powder and milk in a saucepan (I always use the same one, just rinsing it out first). When it's smooth, remove from heat and beat in the powdered sugar until smooth and not lumpy, then add the vanilla and pecans.
As soon as the cake comes out of the oven, gently pour the warm frosting over the top, smoothing it with a spatula to cover the entire cake.
Let sit for 30-60 minutes before serving.
Adapted from Joy the Baker