Creating your Texas Sheet Cake is a breeze if you follow these easy steps:

1. Preheat Oven: Start by preheating your oven to 350°F (175°C). Grease and flour a 18×13 inch sheet pan.
2. Mix Dry Ingredients: In a large bowl, sift together the flour, sugar, baking soda, and salt until well combined.
3. Heat Butter and Cocoa: In a saucepan, melt the butter over medium heat. Add the water and cocoa powder, whisking until smooth and heated through. Remove from heat.
4. Combine Mixtures: Pour the chocolate mixture into the flour mixture and stir until just combined.
5. Add Wet Ingredients: Incorporate the buttermilk, eggs, and vanilla extract into the batter. Mix until smooth and well incorporated.
6. Pour Batter: Pour the batter evenly into the prepared sheet pan.
7. Bake: Place the pan in the oven and bake for 20-25 minutes or until a toothpick comes out clean from the center.
8. Cool: Once baked, remove from the oven and let it cool in the pan for about 30 minutes before frosting.
9. Prepare Frosting: While the cake is cooling, in a saucepan, melt the butter for the frosting. Stir in the cocoa and buttermilk, then remove from heat.
10. Mix in Sugar: Whisk in the powdered sugar and vanilla until smooth and glossy. Fold in the optional chopped pecans if desired.
11. Frost the Cake: Once the cake is cooled, pour the warm frosting over the top and spread it smoother with a spatula.
12. Serve: Allow the frosting to set for a few minutes before slicing into squares and serving.