If it were up to my son, Everett, he would survive on blueberries alone, so I knew I had to include a blueberry cake in this book just for him. I tend to swirl on pink frosting or add buttercream flowers to dress up a cake, so I had extra fun designing this more masculine yet kid-friendly cake. The starry pattern on a background of space-hued swirls reminds me of a galaxy far, far away.
Lemon Poppy Seed Cake
Vanilla and Blueberry Buttercreams
Whipped Vanilla Buttercream
Assembly and Decoration
Cook's Note: Stir any leftover blueberry juice into lemonade or drizzle over ice cream!
Preheat the oven to 350°F (175°c). Grease and flour three 8-inch (20-cm) cake pans and line the bottoms with parchment paper.
Sift together the flours, baking powder, baking soda, and salt into a large bowl. Stir in the poppy seeds. In a small bowl, rub the sugar and lemon zest together between your fingertips until fragrant. In a separate bowl or liquid measuring cup, combine the sour cream and milk.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed for 2 minutes. Add the sugar-zest and mix on medium-high until light and fluffy, 3 to 5 minutes. Stop the mixer and scrape down the bowl.
Turn the mixer to medium-low and add the vanilla. Add the egg whites a little at a time, mixing until each addition is incorporated before adding the next. Add the lemon juice and mix until combined. Stop the mixer and scrape down the bowl.
Turn the mixer to low and add the flour mixture in two batches, alternating with the milk mixture, beginning and ending with the flour mixture. After the last streaks of the flour mixture are combined, mix on medium for no more than 30 seconds.
Evenly divide the batter among the prepared pans. Bake for 23 to 28 minutes, until a toothpick inserted into the center of each cake comes out clean. Let the cakes cool in their pans on a wire rack for 10 to 15 minutes before removing from the pans. Allow the cakes to cool completely, right-side up, on the wire rack before removing the parchment. Level the tops of the cakes with a long serrated knife as needed.
Put 2 cups (480 ml) of the buttercream into a medium bowl or the bowl of a stand mixer for the blueberry buttercream; set aside the remaining buttercream.
In a small saucepan, combine the blueberries and lemon juice and bring to a simmer over medium heat, 5 to 10 minutes. Strain the mixture through a fine-mesh sieve set over a bowl. Press down on the blueberries with a rubber spatula to extract all their juices. Discard the solids in the strainer. With a handheld mixer or using a stand mixer fitted with the paddle attachment, beat together the 2 cups (480 ml) buttercream and 2 tablespoons of the blueberry juice. Add another tablespoon of blueberry juice to deepen the color, if desired. the buttercream should be vibrant in color but not runny.
In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl using a handheld mixer), beat the butter on medium speed until smooth and creamy.
With the mixer running on low, slowly add all but 1 cup (125 g) of the confectioners’ sugar, the milk, and vanilla. Once incorporated, turn the mixer up to medium-high and mix for 3 to 5 minutes, until the buttercream is white, fluffy and smooth. Add the remaining 1 cup (125 g) confectioners’ sugar as needed ⅓ cup (30 g) at a time, until the desired consistency is reached; the buttercream should be soft and spreadable, but not runny.
Whipped vanilla buttercream can be made in advance and stored in a lidded container or wrapped tightly in plastic at room temperature up to overnight, in the refrigerator for 1 to 2 weeks, or in the freezer for up to 3 months. Bring the buttercream to room temperature and mix until smooth before using.
Place one cake layer on a cake board or serving plate. Fill a piping bag fitted with a large round tip with vanilla buttercream. Pipe a ring around the top edge of the cake to create a “dam.” Set aside about 3 tablespoons of the blueberry buttercream, then fill the ring with half of the remaining blueberry buttercream and smooth out with an offset spatula or the back of a spoon. Top with a second cake layer and repeat; place the final cake layer on top.
Crumb coat the cake with the plain vanilla buttercream and chill it in the refrigerator for 15 minutes.
Set aside 1/2 cup (30 ml) of the vanilla buttercream, then frost the cake with the remaining buttercream. The final coat does not need to be perfectly smooth. Divide the reserved ½ cup (30 ml) buttercream between two small bowls; tint one blue and the other lavender. To decorate the cake with the watercolor frosting technique, use a small offset spatula to randomly add small dabs of the colored buttercreams, including the remaining blueberry buttercream, around the sides and top of the cake.
Hold an icing smoother so that it is gently touching the side of the cake, as perpendicular to the cake board as possible. Spin the cake stand so that it rotates one full time around. Clean off the icing smoother and repeat. Fill in any gaps with any remaining buttercream.
Smooth out the cake until a watercolor effect is created. using a small offset spatula, smooth out the top of the cake by gently dragging any raised edges toward the center of the cake. Gently place the edge of the icing smoother on top of the cake (see page 271) or an offset spatula held as flat as possible. Spin the cake stand and smooth out the top of the cake. Using a pastry brush or clean paintbrush, brush the berries with the gold and silver luster dusts.
Arrange the berries in a crescent shape around the top of the cake. Sprinkle with sugar pearls, dragées, and/or sanding sugar as desired.
If eating the cake the same day as assembled, store it at room temperature until ready to serve. If assembled in advance, store in a cake box in the refrigerator overnight. Bring to room temperature for 30 minutes before serving. Store leftovers loosely covered with plastic wrap in the refrigerator for 3 to 4 days.