Step 1

Preheat oven to 350°F. Spray 2 (8-inch) nonstick round cake pans with baking spray; set aside.

Step 2

Beat egg whites in bowl of a stand mixer fitted with the whisk attachment on medium-high speed until stiff peaks form, about 2 minutes. Transfer to a medium bowl, and set aside.

Step 3

Wipe mixer bowl clean. Beat egg yolks and sugar on medium-high speed until doubled in volume and glossy, 5 to 8 minutes. Reduce speed to medium; gradually add milk. Add lemon zest and juice, beating until combined, stopping to scrape down sides of bowl as needed. Gradually add cooled melted butter, beating until smooth, about 1 minute.

Step 4

Sift flour, baking powder, and salt in a medium bowl; add to egg yolk mixture in 2 additions, folding until just combined after each addition. Gently fold in beaten egg whites in 3 additions, folding until just combined after each addition. Divide batter evenly among prepared pans.

Step 5

Bake in preheated oven until cakes are light golden brown and spring back when touched, about 20 minutes. Let cool in pans 10 minutes. Invert cakes onto a wire rack, and let cool completely, about 1 hour.

Step 6

Place 1 cake layer on a cake plate. Using an offset spatula, spread 1 1/2 cups blueberry-coriander buttercream frosting from the center of the cake outward, forming a 1/2-inch-thick frosting layer with a 1-inch-wide, 3/4-inch-tall border around the perimeter to encase the curd. Spoon Meyer lemon curd in center of frosted layer; spread to edges of frosting border. Top with remaining cake layer. Spread a thin layer of frosting over top and sides of cake. Refrigerate 15 minutes. Spread remaining frosting in a thick layer over top and sides of cake. Garnish with blueberry-coriander jam, blueberries, kumquats, lemon, mint, and edible flowers.