Step 1: Preheat and Prepare the Pan

Preheat your oven to 350°F (175°C). Grease a 13×18 inch sheet pan (or a 9×13 inch pan if you prefer a thicker cake) with butter or non-stick spray. Make sure the entire pan, including the sides, is well-greased.

Step 2: Create the Chocolate Base

In a medium saucepan, melt 1 cup of unsalted butter over medium heat. Add 1 cup of water and ¼ cup of cocoa powder. Stir the mixture until smooth and bring it to a boil. Once boiling, remove from heat and set aside to cool slightly.

Step 3: Mix Dry Ingredients

In a large mixing bowl, whisk together 2 cups of flour, 2 cups of sugar, 1 teaspoon of baking soda, and ½ teaspoon of salt. Whisk until fully combined and no lumps remain.

Step 4: Combine Wet Ingredients

In a separate small bowl, lightly beat the eggs. Mix in ½ cup of sour cream and 1 teaspoon of vanilla extract. Pour this mixture into the dry ingredients, along with the slightly cooled chocolate mixture, and stir until everything is combined into a smooth batter.

Step 5: Bake the Cake

Pour the batter into the prepared sheet pan, spreading it evenly with a spatula. Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. While the cake is baking, prepare the frosting.

Step 6: Make the Frosting

In a medium saucepan, melt ½ cup of butter over medium heat. Stir in ¼ cup of cocoa powder and 6 tablespoons of milk. Bring the mixture to a simmer, stirring constantly. Remove from heat, then gradually whisk in 4 cups of powdered sugar until the frosting is smooth and free of lumps. Stir in 1 teaspoon of vanilla extract. If you’re using pecans, fold them into the frosting now.

Step 7: Frost the Cake

Once the cake is done, remove it from the oven and pour the warm frosting over the cake immediately. Spread it evenly with a spatula to cover the entire surface. Let the cake cool for about 20-30 minutes before serving.