This mermaid buttercream cake is made with tender vanilla cake layers and creamy vanilla buttercream that looks like mermaid scales.
Note: I suggest making the fondant mermaid tail before baking the cake or make the tail the day before you decorate the cake. This way it can dry thoroughly while you are getting everything else done.
Depending on the thickness and humidity of the fondant mermaid tail, this can take an average of 4-12 hours to thoroughly dry. You can mix in tylose powder to stiffen and dry the fondant faster. If the fondant mermaid tail isn’t dry enough then gravity will take over and break it off the support skewer.
On the silicone fondant mat, roll out the light purple fondant to a thickness of 3/16 inch - 1/4 inch. If the fondant is a little sticky, then use a small amount of cornstarch.
Next, use a Fondant Mermaid Tail Stencil to cut out the shape of the tail. Use a sharp knife like an X-Acto knife to get clean edges.
Insert a wooden skewer running through the center of the tail to help the tail stand up easier inside the cake.
Then smooth the cut edges with a small amount of shortening and use a pointed fondant molding tool to create the signature tail fin lines.
Set the fondant tail aside on a piece of parchment paper to dry thoroughly depending on how thick the piece of fondant is. If your fondant is mixed with tylose powder, then this process can take at least 2 hours, or it’ll take up to 4 hours to dry normally.
Preheat oven to 350 °F. Spray three 6-inch round cake pans or two 8-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.
In a medium-size bowl, whisk and stir together the all-purpose flour, cornstarch, baking powder, and salt. Set aside.
In the stand mixer bowl fitted with a paddle attachment, beat the butter, oil, and sugar on medium-high for 5 minutes.
Add the eggs, one at a time to the stand mixer bowl and beat on medium until well incorporated.
Turn the mixer on low and add the flour mixture to the butter mixture until fully incorporated.
Pour in the buttermilk and add vanilla extract.
Divide the cake batter into three equal parts. Then color each bowl of cake batter. In one bowl, add purple gel food color, in the second bowl add sky blue gel food color and in the final bowl add neon green and leaf green gel food color. Mix the cake batter and food color with a rubber spatula and scrape down the sides of the bowl.
Evenly divide the colored cake batter into the three 6-inch cake pans. Use a wooden skewer to swirl the three colored cake batter together into each pan.
Bake for about 35-40 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.
Remove cakes from oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely — wrap cakes in plastic wrap and place in the freezer to chill for 30 minutes.
In the stand mixer bowl fitted with the paddle attachment, beat the butter until light and fluffy, about 5 minutes.
Turn the mixer to low and gradually add the powdered sugar, followed by the heavy cream, salt and vanilla extract. Mix until incorporated completely. Scrape down sides of the bowl.
Turn the mixer to medium-high and beat the buttercream for about 5 minutes until light and fluffy.
Turn the mixer on low and mix for 2 minutes to push out any air bubbles.
Divide the buttercream into three bowls and color one bowl of buttercream light purple, one bowl of buttercream a light green and one bowl of buttercream a light blue.
Then prepare three piping bags with round piping tips and filled 2/3 of the way with buttercream.
Remove the cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.
Add a small amount of buttercream onto the center of the cake board. Layer the chilled mermaid marbled cake, cut side up onto the cake board.
Then pipe a ring of blue buttercream to the outside edge of the cake, followed by the purple buttercream and in the center pipe the green buttercream. Use an offset spatula to smooth the layer of buttercream.
Place another cake layer cut side down over the top. Repeat the process for another layer — Crumb coat and freeze for 20 minutes.
Starting from the bottom of the cake, pipe a single dot about 1-inch of the buttercream. Use an offset spatula to press and pull the dot towards the side of the cake. Then pipe another dot above the previous dot. Repeat the process until you have one column completed.
To start a new column, pipe the next dot overlapping the previous pulled dot. Alternate the colors to create a scale effect. Repeat the process all over the whole cake. Place the cake into the fridge to set the buttercream.
Then mix 1/2 tsp of gold highlighter luster dust and one drop of clear alcohol (lemon extract) until it looks like paint. Then with a small brush, paint the edge of random buttercream scales to give a shimmer effect.
Paint the gold luster dust on the edges of the mermaid tail for the finishing touches. Then carefully insert the tail into the center of the cake, standing up straight to complete the cake.