A delicious, moist Texas sheet cake infused with rich cocoa flavor, sour cream and topped with a rich chocolate icing. This particular version is the version I've made since I was a teenager. Not exactly like mom's ... but close.
Preheat oven to 350 degrees. Spray a jelly roll pan with cooking spray.
On the stove, melt the butter. Add the hot water and then the cocoa. Bring to a boil. Remove from heat once it's boiling.
While waiting for that to boil, in a large bowl, whisk the flour, sugar, baking soda and salt until blended. Pour the boiling liquid into the dry ingredients and blend. Add sour cream and stir to blend.
Pour the batter into a standard size jelly roll pan. Bake in a 350 degree preheated oven for 20 minutes. Check to make sure it's done with a toothpick inserted near the center.
Once it's done, remove from oven and set aside to begin cooling.
For Icing:
In a saucepan on the stove, melt the butter.
Add the milk, vanilla and cocoa and bring to a boil. Once boiling, remove from the heat.
Whisk in the powdered sugar. I usually sift it first because if you don't blend it in really well, you will get little pebbles of sugar in there. They don't look pretty, but they taste fine - so don't stress.
Stir in the sour cream until smooth.
Nuts are optional and pecans can be substituted instead of walnuts.