At every family and church function, I take my chocolate sheet cake. Iād like to occasionally do something different, but itās always in such high demand. It really is that good, but the best thing is that itās simple to make, and I usually have the ingredients on hand. Itās large, so it feeds a crowd, too. Oh, and you donāt have to drag out the mixer for this one. 
Chocolate Sheet Cake
In a large bowl, mix together:
[color=red]2 cups sugar
2 cups flour
1 tsp salt (unless you donāt use unsalted butter, then use only 1/2 tsp salt)
1 tsp baking soda[/color]
In a medium saucepan, bring just to a boil:
[color=red]1 stick butter
1/2 cup vegetable oil
1 cup water
4 TBSP cocoa[/color]
After removing from the heat, slowly stir the hot mixture into the large bowl with the dry ingredients.
In a separate small bowl, mix together:
[color=red]2 lightly beaten eggs
1/2 to 1 cup buttermilk (Iāve used both amounts with no discernable difference)
1 tsp vanilla[/color]
If you donāt have buttermilk, simply add a teaspoon of white vinegar to your milk, and let it sit a few minutes. I rarely have buttermilk on hand, so this is what I usually do.
Gradually stir the egg/milk mixture into your large bowl of ingredients.
Pour into an oiled (use non-stick cooking spray, or coat with veggie oil) jellyroll pan. Iām not sure of the exact ingredients, but itās about 10" x 15". If you donāt have one of these, you should go to Wal-Mart and buy one. Once you make this cake once, youāll be wanting to make it again and again, and the pan is perfect for it.
Bake at 400 for about 20 minutes. Because this pan is so large and shallow, the cake bakes very quickly!
Test for doneness by lightly touching the center of the cake.When it springs back to your touch, and the corners are just beginning to pull away from the pan, itās done.
For the frosting; during the last 5 minutes of baking time, in a medium saucepan, bring to a boil:
[color=red]1 stick butter
5 TBSP milk
4 TBSP cocoa[/color]
When it begins to boil, remove it from the heat and stir in:
[color=red]1 tsp vanilla, then[/color]
[color=red]1 16oz box of confectionerās (powdered) sugar, then
1 cup chopped pecans[/color]
When you remove the cake from the oven, while itās still warm, gently spread the icing over the cake.
Scrape the remaining bits out of the frosting pan and eat it before running water in it to soak, as it tastes just like chocolate fudge! 
If you donāt have a jellyroll pan, and donāt wish to purchase one, you can bake this in a regular cake pan. Cut the oven temp back to 350, and it will take longer to bake. Iām not sure of the exact time, but you could watch it closely-probably about 30 minutes. I have baked it this way when my jellyroll pan was on loan to my mom, but I finally bought a new pan so weād each have one. 