Preheat your oven to 350F degrees. Lightly grease and flour a 9×13 inch baking pan. This initial step is crucial as it will ensure your cake doesn’t stick and comes out beautifully.
In a medium saucepan over low-medium heat, add the unsalted butter, cocoa powder, and water. Melt everything together while gently whisking until the cocoa powder is fully dissolved and the butter is melted. Take it off the heat and let it cool slightly.
Pour the melted mixture into a large mixing bowl. This is where the magic begins! Allow it to cool for a few moments before moving on to the next step.
Mix in the granulated sugar until well combined, followed by adding the eggs and vanilla extract. You’ll want to use a whisk or mixer for a smooth texture here.
With the mixer on low, gradually add in the all-purpose flour, baking soda, and salt. The batter will start to take shape as you mix. Finally, fold in the sour cream for that signature moisture.
Pour the cake batter into the prepared pan, smoothing the top with a spatula. This is the moment you wait for—baking magic is about to happen!
Bake in your preheated oven for about 35 minutes. Keep an eye on it; a toothpick inserted in the center should come out clean. I usually start checking around 30 minutes just in case.
While the cake is baking, prepare the frosting. In a small saucepan, melt together the unsalted butter and cocoa powder over medium heat, stirring until smooth. Then remove it from the heat.
Pour the melted mixture into a mixing bowl and allow it to cool slightly. Once cooled, beat in the powdered sugar, about 1/2 cup at a time, alternating with a tablespoon of milk until you reach the desired consistency. Remember, you want a frosting that spreads easily but isn't too runny.
Once the cake is completely cooled, frost it generously with the chocolate frosting, and if you're feeling fancy, decorate it with sprinkles. Serve and enjoy the smiles!