Blackberry Elderflower Vertical Layer Cake

Preheat the oven to 350°F (175°C). Grease two 13×18” (33x46cm) pans and line the bottoms with parchment paper. In the bowl of a stand mixer fitted with the whisk attachment, beat the eggs and granulated sugar on medium-high speed until the mixture triples in volume, about 8 minutes. Stop the mixer and sift in the flour, cornstarch, baking powder and salt. Using the mixer’s whisk, stir the mixture by hand until combined.

In a separate bowl, stir together about a cup (240ml) of the mixture and the melted butter. Add the vanilla, pour back into the bowl with the remaining mixture and gently fold to thoroughly combine. Evenly divide between the pans and bake for 12-15 minutes until the surface springs back when gently touched. Rotate halfway through baking. Do not overbake or the cakes may crack.

Dust the warm cakes with a generous amount of confectioners’ sugar. Place a clean tea towel on top of each cake. Carefully flip the pans upside down to release onto the towels. Peel off the parchment paper and dust the bottoms with confectioners’ sugar. While still warm, roll them up in the towels starting at the short ends. Set seam side down and let cool completely in the towels, 30-45 minutes. Once cooled, carefully unroll and remove the towels. Like muscle memory, the cake will remember to retain its curved shape once cooled.

FOR THE ELDERFLOWER SYRUP:

In a small saucepan, combine the sugar, elderflower liqueur, lemon juice and two tablespoons of water and bring to a boil. Reduce the heat to low and simmer for about 5 minutes. Remove from the heat and set aside to cool.

FOR THE WHIPPED VANILLA BUTTERCREAM:

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 750g of the confectioners’ sugar, milk and vanilla. Once incorporated, turn the mixer up to medium-high and mix for 3-5 minutes until the buttercream is white, fluffy and smooth. Add the remaining 125g of confectioners’ sugar as needed 30g at a time until the desired consistency is reached; the buttercream should be soft and spreadable but not runny.

FOR THE BLACKBERRY BUTTERCREAM:

In a small saucepan, combine the blackberries and lemon juice and bring to a simmer over medium heat, 5-10 minutes. Using a submersion blender, puree the cooked blackberries (be careful as this can be messy). Alternatively, smash with a potato masher or the back of a slotted spoon. Strain through a fine sieve set over a bowl. Press down on the puree with a rubber spatula to extract all the juice. Discard the solids in the strainer. Set the strained puree aside and cool. With a handheld mixer or a stand mixer fitted with the paddle attachment, beat together the buttercream and 4-6 tablespoons of the blackberry puree a few tablespoons at a time. The buttercream should be soft and spreadable but not runny.

ASSEMBLE THE CAKE

Cut the cooled cakes in half lengthwise to create four long strips of cake. Generously brush with the elderflower syrup. Spread the blackberry buttercream on top of each strip with a small offset spatula using about 180ml of the buttercream per strip. Gently roll up a strip to make a spiral. Turn on its side and begin wrapping the remaining cakes around the centre spiral, setting the start of each at the end of the last to create a large spiral of cake and filling. Place on a cake board or serving plate. Crumb coat with the buttercream and chill in the refrigerator for 15 minutes.

FOR THE DECORATION:

Set aside about 120ml of the remaining buttercream. Remove the cake from the refrigerator and smoothly frost with the blackberry buttercream. Tint half of the reserved buttercream with a bit of blackberry puree or gel food colouring to create two shades of purple. To create the buttercream flowers, fill a piping bag fitted with a medium closed star tip (such as Wilton 2B) with the two shades of remaining buttercream. Use a small offset spatula to place the two shades on either side of the piping bag (it is okay if they aren’t perfectly divided—the swirl of colour will give the piped flowers more dimension). Holding the piping bag perpendicular to the surface of the cake, pipe clusters of flowers on the top and sides of the cake or as desired. Place a sugar pearl in the centre of each flower.