Set your oven to 350°F (175°C). Thoroughly grease a 10-cup Bundt pan with either butter and flour or nonstick spray. This helps the cake come out cleanly after baking.

In a large bowl, combine the vanilla cake mix, instant vanilla pudding mix, eggs, water, sour cream, and oil. Use a hand or stand mixer on medium speed to blend everything together for about 2 to 3 minutes until smooth. Be sure to scrape the bowl’s sides to mix all ingredients evenly.

Pour the batter into the prepared Bundt pan, smoothing it out evenly. Give the pan a gentle tap on the counter to release air bubbles. Bake for 45 to 50 minutes, or until a toothpick inserted in the center comes out clean. The cake should be golden on top and spring back lightly when pressed.

Let the cake rest in the pan for 15 to 20 minutes after removing it from the oven. Then, carefully flip it onto a wire rack to cool completely. Avoid frosting while the cake is warm to prevent melting.

Beat together softened butter and cream cheese until creamy and smooth. Slowly add powdered sugar while mixing on low to keep the sugar dust down. Once combined, pour in the buttermilk and increase the speed to medium-high. Continue beating until the frosting is fluffy yet thick enough to pipe.

When the cake has fully cooled, fill a piping bag with the frosting. Use a round or ribbon tip to pipe thick lines from the center outward, replicating the signature Bundt cake style. If you don’t have a piping bag, spreading the frosting evenly works just fine.