Preheat your oven to either 350 degrees or the temperature specified in your recipe.

Prepare your cake pans by either greasing them with butter and flour or using your preferred baking spray, then set them aside.

Combine the cake mix, flour, cocoa powder, eggs, oil, water, and vanilla in a large mixing bowl. Begin mixing on low speed for a minute until the ingredients are blended.

Turn the mixer to medium speed and mixing for two minutes. Afterward, switch off the mixer, scrape the bowl sides, and resume mixing if necessary. Use a spatula to mix in the sour cream.

Divide the batter equally among the pans and insert them into the oven to bake as per the instructions on the cake mix box.

To ensure your cake is done, begin checking it as soon as the time recommended on the box has elapsed. Insert a toothpick or cake tester into the center of the cake to check for doneness. If there are only a few crumbs on the tester, the cake is ready. If the batter is still wet, return the cake to the oven and check it every five minutes.

After the cake is finished baking, take the pans out of the oven and allow them to cool.

Combine the canned chocolate frosting, vanilla, powdered sugar, and butter in a bowl of medium size.

Begin mixing the ingredients together by turning on the mixer at a low speed. Gradually elevate the speed to medium and ensure that all the ingredients are well combined.

After turning off the mixer, examine the frosting to ensure it has the desired thickness. If it falls short, incorporate additional powdered sugar, then restart the mixer and blend until you achieve the desired consistency.

Begin frosting your cake after it has cooled down and the frosting is prepared.

First, put the bottom layer of cake on the stand. Spread 1/4 cup of frosting on top of it. Frost the top layer and then add another 1/4 cup of frosting to frost it. Finally, use the rest of the frosting to cover the sides.