Preheat Your Oven: Set your oven to 350°F (175°C). vbcv Prepare a 13x18-inch sheet pan by greasing it lightly with butter or non-stick spray.

Combine the Dry Ingredients: In a large mixing bowl, whisk together 2 cups of all-purpose flour, 2 cups of granulated sugar, 1 teaspoon of baking soda, and 1/2 teaspoon of salt. Set this mixture aside.

Prepare the Chocolate Base: In a medium saucepan, melt 1/2 cup of unsalted butter, 1/2 cup of vegetable oil, 1 cup of water, and 1/4 cup of unsweetened cocoa powder over medium heat. Stir frequently until the butter is fully melted and the mixture is smooth. Allow the mixture to come to a gentle boil, then remove it from the heat.

Mix the Wet and Dry Ingredients: Pour the hot chocolate mixture into the bowl with your dry ingredients. Stir until the mixture is well combined.

Add the Buttermilk and Eggs: In a small bowl, whisk together 2 large eggs, 1/2 cup of buttermilk, and 1 teaspoon of vanilla extract. Pour this into the chocolate batter and stir until everything is fully incorporated and smooth.

Bake the Cake: Pour the batter into your prepared sheet pan, spreading it evenly. Bake in the preheated oven for 15-20 minutes. The cake is ready when a toothpick inserted into the center comes out clean.

In a Medium Saucepan: While the cake bakes, prepare the frosting. In a medium saucepan, melt 1/2 cup of unsalted butter over medium heat. Stir in 1/4 cup of unsweetened cocoa powder and 1/4 cup of milk. Continue stirring until smooth. Remove the saucepan from the heat, then gradually mix in 3 1/2 cups of powdered sugar and 1 teaspoon of vanilla extract until the frosting is smooth and glossy. If you like, stir in 1 cup of chopped pecans for added texture and flavor.

Frost the Cake: As soon as the cake comes out of the oven, pour the warm frosting over the hot cake. Use a spatula to spread the frosting evenly across the surface.

Cool and Serve: Allow the cake to cool in the pan on a wire rack. Once cooled, slice the cake into squares and serve. The cake can be stored at room temperature in an airtight container for up to 3 days.