Rainbow Cake Roll

A stunning rainbow cake roll made with a cake mix and filled with sweet vanilla buttercream frosting.

Author Amber Brady

Prep Time 1

Cook Time 17

Rest Time 1 45

Total Time 3 2

Yields servings

Ingredients

Cake Batter:

⅔ cup (160 g) sour cream, room temperature
¾ cup (177 ml) buttermilk, room temperature
1 Tbsp pure vanilla extract
4 egg whites, room temperature
⅓ cup (80 ml) oil, canola/vegetable
1 (15.25)oz (432 g) box white cake mix, I use Duncan Hines
food coloring gel, red, orange, yellow, green, blue, and purple

Vanilla Buttercream Frosting:

1 cup (226 g) unsalted butter, (2 sticks) room temperature
¼ tsp salt
4 cups (480 g) powdered sugar
2 tsp pure vanilla extract
4 Tbsp heavy cream, or milk

Instructions

Preheat the oven to 325℉. Line a half sheet pan (13×18-inches) with parchment paper, leaving a couple inches of overhang to easily lift the cake out of the pan. Optional: Spray the parchment-lined baking sheet with Baker’s Joy — a nonstick baking spray with flour in it. (This helps release the cake in addition to the parchment paper.) Set pan aside.
Make the Cake Batter: Place the sour cream, buttermilk, vanilla, egg whites, and oil in a large bowl. Whisk together until combined well. Sift the white cake mix into the bowl of wet ingredients. Stir together until just combined. (Do not over-mix.)
Divide and Color Batter: Divide the cake batter into six small bowls; about 2/3 cup of batter in each. Add food coloring (I use AmeriColor gels) and mix colors separately. (Red, orange, yellow, green, blue, and purple.) Fill piping bags with individual colors. It’s easiest to do this by using a glass cup to cuff the top of the bag over the rim. Then fill it with cake batter, remove the bag, and twist the top. NOTE: Do not cut the ends until ready to pipe.
Pipe Stripes: Cut the tips off the bags and pipe the colors diagonally across the prepared pan in the order of a rainbow: red, orange, yellow, green, blue, and purple. TIP: Pipe thin layers to begin with so you don’t run out of cake batter. Then go back over any areas that may need extra.
Bake: Tap the baking sheet on the counter to remove any air bubbles and to help the different colored stripes settle into one-another. Bake the rainbow cake roll at 325℉ for 17 minutes or until baked through.
Rolling & Cooling: Immediately lift the cake out of the pan with the parchment paper and set it on a wire rack (or two, to make sure the cake doesn’t dangle off the edges and crack). Allow the cake to let off steam for 4 minutes. (Set a timer! Timing is important.) Then roll the cake up while it’s still warm starting from one of the shorter (13-inch) sides. TIP: I like to fold any excess paper to make it about 1-inch thick, then fold it on top of the cake, and then use the edges of the paper to continue rolling it up tightly without squishing the cake. Let the cake cool completely at room temperature; about 40 minutes.
Make the Vanilla Buttercream Frosting: Using an electric mixer and the paddle attachment beat the butter with the salt until creamy. Add the powdered sugar, 1 cup at a time, mixing completely before adding more. Repeat until all powdered sugar is added. Mix in the vanilla. Add the heavy cream or milk 1 Tablespoon at a time while mixing, until the desired consistency is reached.
Slowly and carefully unroll the cake. You may need to use a spatula to gently scrape off any cake that sticks to the paper due to the condensation.
Filling: Dollop the frosting over the cake. Use an offset spatula to smooth the icing over the cake leaving 1/2-inch bare on the end you will roll towards. NOTE: Icing will seem thin. TIP: Keep the tip of the spatula in the frosting the whole time as to not lift crumbs into the frosting.
Re-roll the cake as tightly as you can. Pulling the cake away from the parchment paper as needed. TIP: Start rolling the cake with your fingers, then lift the parchment paper to help roll the cake. *See photos in post.
Chilling: Wrap the cake roll with plastic wrap and freeze it for 1 hour or until firm. Alternately freeze the cake overnight. TIP: Leave the cake on the parchment paper and cut off the excess. Then use the edges of the remaining paper to lift the rolled cake onto the plastic wrap to be wrapped completely. This will help prevent any extra cracking from the delicate cake.
Unwrap the chilled cake. Use a hot knife to cut the rainbow cake roll into 3/4-inch slices; about 16 pieces. TIP: Rinse and dry the knife between cuts for clean slices. NOTE: Cake slices will thaw in about 15 minutes at room temperature.

Notes

Double wrap the cake if freezing for longer than 24 hours.
Frosting makes about 3 cups.
Store any leftover cake slices wrapped well in the refrigerator.

Nutrition