Lemon Curd Filling

1. Measure 2 teaspoons lemon juice into small bowl; sprinkle gelatin over top. Heat remaining lemon juice, sugar, and salt in medium nonreactive saucepan over medium-high heat, stirring occasionally, until sugar dissolves and mixture is hot but not boiling. Combine eggs and yolks in large nonreactive bowl, whisk to combine. Continue to whisk and slowly pour hot lemon-sugar mixture into eggs, then return mixture to saucepan. Cook over medium-low heat, stirring constantly with heatproof spatula, until mixture registers 170℉ and is thick enough to leave trail when spatula is scraped along pan bottom, about 5 minutes. Immediately remove pan from heat and stir in gelatin mixture until dissolved. Stir in frozen butter until incorporated. Pour filling through fine-mesh strainer into nonreactive bowl. Cover surface directly with plastic wrap; refrigerate until firm, at least 4 hours.

Blue Coconut Cake

1. Adjust oven rack to middle position and heat oven to 350℉. Spray two 9-inch-round cake pans with nonstick cooking spray; line bottoms with parchment rounds. Spray paper rounds, dust pans with flour, and knock out excess, set aside.

2. Whisk 2 cups flour, baking powder, and salt together in medium bowl. In the bowl of a stand mixer fitted with paddle attachment, beat butter and sugars on medium-high speed until fluffy, about 2 minutes. Add eggs, one at a time, beating until just incorporated. Add coconut extract and beat to combine.

3. With mixer running at low speed, add flour mixture in 3 additions, alternating with coconut milk  (in 2 additions), beginning and ending with flour mixture, and beating in each addition until barely combined. Remove bowl from mixer, gently stir in blueberries and shredded coconut by hand with rubber spatula, scraping bottom and sides of bowl, to ensure that batter is homogenous. Divide batter evenly between prepared cake pans; spread batter to edges of pans with rubber spatula and smooth surfaces. Bake until toothpick inserted in center of cakes come out clean, 45-50 minutes. Cool in pan for 20 minutes and invert cake onto cooling rack and continue to cool completely.

Whipped Cream Frosting

1. Sprinkle powdered gelatin over water in a microwave-safe bowl and let it stand for 3 minutes. Microwave the mixture in 5-second increments until the gelatin is dissolved and liquefied. In the bowl of a stand mixer fitted with a whisk attachment, whisk chilled heavy cream, sugar and vanilla extract on low speed until foamy with small bubbles. Increase speed to medium and continue to whisk until slightly thickened; slowly pour in the gelatin mixture and then increase the speed to high and continue to beat until soft peaks form. Use immediately or cover and chilled in refrigerator for up to 1 day.

Assembly

2. Trim top of each cake layer to level, place one cake layer on a cake stand or serving platter, Spread 1/2 of the filling over cake layer and top with another layer. Repeat with remaining filling. Pipe or spread frosting evenly over top edge and sides of cake. Sprinkle top with blueberry powder (if use).

Chocolate Cake

1. Adjust oven rack to lower-middle position; heat oven to 350℉. Combine chocolate, cocoa and espresso powder in small bowl; pour boiling water over and let stand to melt chocolate, about 30 seconds. Whisk until smooth; set aside until cooled to room temperature.

2. Spray three 8-inch-round cake pans with nonstick cooking spray; line bottoms with parchment rounds. Spray paper rounds, dust pans with flour, and knock out excess. Combine flour and baking soda in a small bowl, set aside.

3. In bowl of standing mixer fitted with paddle attachment, beat butter, sugars, and salt at medium-low speed until sugar is moistened, about 30 seconds. Increase speed to medium-high and beat until mixture is light and fluffy, about 3-4 minutes, scraping down bowl with rubber spatula as needed.

4. Reduce speed to medium, add eggs one at a time, beating well after each addition, scrape down bowl as needed. Reduce speed to low, add vanilla and room temperature chocolate mixture, then increase speed back to medium and beat until combined, about 30 seconds.

5. With mixer running at low speed, add dry ingredients in 3 additions, alternating with sour cream (in 2 additions), beginning and ending with dry ingredients, and beating in each addition until barely combined. Stir by hand with rubber spatula to finish mixing batter, scraping bottom and sides of bowl, to ensure that batter is homogenous (batter will be thick). Divide batter evenly between prepared cake pans; spread batter to edges of pans with rubber spatula and smooth surfaces.

6. Bake cakes until toothpick inserted into center of cakes comes out clean, about 25-30 minutes. Cool in pans for 15 minutes, then invert cakes onto greased wire rack; peel off and discard paper rounds. Cool cakes to room temperature, about 1 hour.

Dulce de Leche Frosting

1. Combine whites, sugar, and salt in bowl of standing mixer; set bowl over saucepan containing 1-1/2-inches of barely simmering water. Whisk constantly until mixture is opaque and warm to the touch and registers about 120℉ on an instant-read thermometer, about 2 minutes.

2. Transfer bowl to mixer and beat whites on high speed with whisk attachment until barely warm. whites are glossy and sticky, about 7 minutes. Reduce speed to medium-high and beat in butter 1 piece at a time. Beat in dulce de leche and vanilla extract. Stop mixer and scrape bottom and sides of bowl. Continue to beat at medium-high speed until well-combined, about 1 minute.

Chocolate Ganache and Assembly

1. Bring cream and corn syrup to a full simmer over medium heat in a small saucepan (alternatively, heat in microwave). Off heat, add chocolate; cover and let stand for 8 minutes. (If chocolate has not completely melted, return saucepan to low heat; stir constantly until melted.) Add vanilla; stir very gently until mixture is smooth. Cool slightly.

2. Trim top of each cake layer to level, place one cake layer on a cake stand or serving platter, Spread about 1 cup frosting over cake layer and top with another layer. Repeat with 1 cup frosting and cake layers. Spread remaining frosting evenly over top and sides of cake. Spread Chocolate Ganache on top of cake and allow chocolate to drip down the side. Decorate with cookies and malt balls (if use), pressing lightly to adhere. Serve. (Cake can be refrigerated for up to 2 days.)