Heat oven to 350F. Prepare 3 6-inch cake pans with parchment circles and baking spray. Set aside.
In the bowl of your stand mixer fitted with the paddle attachment, combine the sugar, oil, eggs and vanilla extract. Beat until fully incorporated and light in color - approximately 2-3 minutes. Add in sour cream and mix to combine. Scrape down the sides of bowl as needed
Whisk together flour, baking powder and salt in a medium bowl. Add half of the flour mixture into the batter and while on low speed, pour in half the milk. Mix until just combined. Repeat with remaining flour and milk. Scrape down the sides of bowl to incorporate fully.
Divide batter between 3 cake pans. For 6-inch pans, bake 30-33 minutes, or until a cake tester inserted into the center comes out clean.
Remove from oven and cool in pans for 10 minutes. Invert onto cooling rack to cool completely. Once cool, wrap in plastic wrap and refrigerate until cool enough to level cakes.
Vanilla Almond Buttercream Instructions
Cut butter into small slices and place into bowl of stand mixer with paddle attachment. Add salt. Whip butter for 5-7 minutes until light and airy. Scrape down sides of bowl as necessary.
Add 3 cups powdered sugar and mix on low to combine. Add in vanilla, butter and almond extracts then combine.
Add 2 cups powdered sugar and mix on low to combine. Scrape down sides as necessary. Add in remaining 2 cups powdered sugar. While on low, add in milk and mix to combine. Beat on medium-high for 5 minutes to whip. Scrape sides of bowl and re-whip if needed.
Level cakes. Place a small amount of frosting on cake board to secure cake. Place bottom layer on cake board. Add frosting to cake and level with offset spatula (approx 1/4 – 1/3 cup). Repeat with second layer.
Place last layer on top upside-down and apply a crumb coat* over cake. Place in freezer for 15-20 minutes.
Remove 2 cups white frosting. Color 1/2 cup dark turquoise, 1/2 cup mint, 1/2 cup mint + turquoise, and 1/2 cup regal purple. 1M for dark turquoise, 1M for regal purple, 8B for mint/turquoise, and 22 for mint.
Color remaining frosting light turquoise. Frost top and sides and smooth with cake scraper/comb. Place in freezer for 15-20 minutes to chill. Place extra into piping bag with Wilton 32 open star tip.
Pipe rosettes onto cake and add sprinkles. Place in refrigerator while making candy mermaid tails. Follow directions on package for mermaid tails. Reserve a small amount of candy coating and use it to adhere small lollipop sticks to the back of two tails. Insert into cake. Place additional tail on the side of the cake.
Serve or refrigerate then bring to room temperature before serving.
* Crumb coat is a thin layer of frosting applied after stacking the cake, so the crumbs do not show when the final layer of frosting is applied.