In mid-2023, we shared a photograph of a similar cake on TeaTime’s social media channels, and our followers fell in love with the image and wanted a recipe for the dessert. What we didn’t know at that time was that the image was generated using artificial intelligence (AI), so there was no recipe to be had. Determined to give our readers what they requested, our editor challenged our Test Kitchen professionals to create a similar cake that wouldn’t just be pretty but would also be delicious and doable. Because the acidity of the lemon zest in the yellow batter will cause the blue pea flower powder in the blue batter to turn purple, it is important to keep the batters separate until they are layered in the pans.
Lemon-Blueberry Layer Cake
Serves: 1 (8-inch) 2-layer cake
Ingredients
- 2⁄3 cup vegetable oil, divided
- 1 cup whole milk, divided, room temperature
- 1 1⁄2 cups granulated sugar, divided
- 4 large eggs, divided, room temperature
- 2 teaspoons vanilla extract, divided
- 1 tablespoon fresh lemon zest
- 1 drop yellow gel food coloring
- 2 1⁄2 cups all-purpose flour, divided
- 1 tablespoon baking powder, divided
- 1⁄2 teaspoon fine sea salt, divided
- 1 tablespoon butterfly pea powder*
- 1 tablespoon finely crushed freeze-dried blueberries
- Swiss Meringue Buttercream, divided (recipe follows)
- 1⁄2 cup blueberry preserves
- Gel food coloring**
Instructions
- Preheat oven to 350°. Spray 2 (8-inch) cake pans with baking spray with flour. Line pans with parchment paper. Spray parchment paper again with baking spray with flour.
- In a large bowl, whisk together 1⁄3 cup oil, 1⁄2 cup milk, 3⁄4 cup sugar, 2 eggs, 1 teaspoon vanilla extract, lemon zest, and yellow food coloring until smooth.
- In a medium bowl, whisk together 1 1⁄4 cups all-purpose flour, 1 1⁄2 teaspoons baking powder, and 1⁄4 teaspoon salt until well combined. Gradually whisk flour mixture into oil mixture until just combined. Divide between prepared pans, and spread in an even layer.
- In another large bowl, whisk together remaining 1⁄3 cup oil, remaining 1⁄2 cup milk, remaining 3⁄4 cup sugar, remaining 2 eggs, and remaining 1 teaspoon vanilla until smooth.
- In a medium bowl, whisk together remaining 1 1⁄4 cups all-purpose flour, remaining 1 1⁄2 teaspoons baking powder, remaining 1⁄4 teaspoon salt, butterfly pea powder, and crushed freeze-dried blueberries. Gradually whisk flour mixture into oil mixture until just combined. Gently spoon blue batter evenly over lemon batter in pans, but do not swirl.
- Bake until cake layers are golden brown and a pick inserted into the centers comes out clean, 25 to 30 minutes. Let cool in pans on wire racks for 10 minutes. Remove cake layers from pans and let cool completely on wire racks.
- If cake layers are domed, trim and discard dome using a large, serrated knife, if desired.
- Reserve 1 cup Swiss Meringue Buttercream for decoration.
- Place one cake layer on a cake stand, yellow side down, and spread 1⁄4 cup buttercream over cake layer top in a thin layer to the edge.
- Place 1⁄2 cup buttercream in a piping bag, and cut a 1⁄2-inch opening from tip. Pipe a 1⁄4-inch border around edge of cake layer. Spread blueberry preserves inside buttercream border. Top with remaining cake layer, yellow side down. Cover top and sides of cake with a thin layer of buttercream. Freeze until firm, 15 to 20 minutes.
- Spread more buttercream in a thick, smooth layer on top and sides of cake.
- Place 1⁄3 cup of reserved 1 cup buttercream in a small bowl, and add gel food coloring to achieve desired lighter blue hue. Transfer buttercream to a piping bag fitted with a small round tip (Wilton #4).
- Place remaining 2⁄3 cup of reserved 1 cup buttercream in another bowl, and add gel food coloring to achieve desired darker blue hue. Transfer buttercream to a piping bag fitted with a small round tip (Wilton #4).
- Pipe both blue buttercreams in scrolling motifs and borders to decorate cake as desired. Serve immediately, or cover with a dome, refrigerate, and serve within a day. Let come to room temperature before serving.
Notes
*We used Wild Hibiscus Flower Company b’Lure Blue Matcha Tea Powder, which is made from butterfly pea flowers, available at wildhibiscus.com.
**We used a combination of Wilton Cornflower Blue, Royal Blue, Purple, and Pink to achieve our desired blue shades for the buttercream scrollwork.
**We used a combination of Wilton Cornflower Blue, Royal Blue, Purple, and Pink to achieve our desired blue shades for the buttercream scrollwork.
Swiss Meringue Buttercream
Serves: approximately 8 cups
Ingredients
- 10 large egg whites
- 2 1⁄2 cups granulated sugar
- 1⁄2 teaspoon fine sea salt
- 1⁄4 teaspoon cream of tartar
- 2 1⁄2 cups unsalted butter, softened
Instructions
- In the heatproof bowl of a stand mixer, whisk together egg whites, sugar, salt, and cream of tartar. Set over a saucepan of simmering water and heat, stirring often, until sugar dissolves and a digital thermometer registers 160°, 5 to 10 minutes.
- Attach bowl to mixer fitted with the whisk attachment. Beat at high speed until cooled, approximately 10 minutes. Reduce mixer speed to medium-high. Beat in butter, 1 tablespoon at a time, until each piece is incorporated before adding more. Continue to beat until mixture thickens, comes together, and is smooth. (Buttercream may look curdled at first, but keep beating.) Use immediately.
