This recipe is from the post: Let Them Eat Cake!

Texas Sheet Cake (slightly adapted from Cooking Light)

Cake:
2 cups all purpose flour, plus extra to flour the pan
2 cups cane sugar or granulated sugar
1 teaspoon baking soda
1 generous teaspoon ground cinnamon
1/4 generous teaspoon kosher salt
3/4 cup water
1/2 cup (1 stick) unsalted butter, plus extra to grease the pan
1/4 cup cocoa
1/2 cup buttermilk
1 teaspoon vanilla, good quality like Madagascar Bourbon
2 large eggs

Icing:
6 tablespoons butter
1/3 cup milk, I used 2%
1/4 cup cocoa
3 cups powdered sugar
2 teaspoons vanilla, good quality
3/4 cup pecans, toasted and then coarsely chopped

Preheat oven to 375 degrees F. Butter a 15 x 10 inch jelly-roll pan and then dust with flour. Set aside. Combine 2 cups of flour, the cane or granulated sugar, the baking soda, cinnamon and salt in a large bowl. In a small saucepan, combine 3/4 cup water, 1/4 cup cocoa and 1/2 cup butter over medium low heat, stirring until it comes to a boil. Remove from the heat and add to the flour mixture. Beat with a hand mixer until well blended. Add the buttermilk, 1 teaspoon of vanilla and the eggs and beat well.

Pour the batter into the prepared pan. Bake for 17-19 minutes or until a wooden toothpick inserted in the center comes out clean. Place cake in pan on a wire rack.

Combine the 6 tablespoons of butter, the milk, and 1/4 cup of cocoa in a saucepan. Bring to a boil over medium low heat, stirring constantly. Remove from the heat and gradually stir in the powdered sugar. Stir in 2 teaspoons of vanilla and the nuts. Spread evenly over the hot cake. Cool completely on a wire rack. Cut into squares.