ingredients

for the cake (makes three 9" round thin layers or three 6" thick layers - I doubled this to make six 9" round thin layers for my cake):

• 4 eggs, separated

• (optional) 1 extra egg white

• 100g granulated sugar

• 80g milk

• 50g oil (I used vegetable oil)

• 1 tsp vanilla extract

• 84g all-purpose flour (alternatively, use 100g cake flour and remove cornstarch)

• 15g cornstarch

• 1 tsp baking powder

for the compote:

• ~2-3 cups frozen berries

• 50g water

• 50g granulated sugar

• (optional) 1 tsp lemon juice

for the whipped frosting:

• 1-1/2 cups heavy whipping cream

• 1/2 cup powdered sugar

• 1 tsp vanilla extract

• optional for stabilization:

  • 1 tsp unflavored gelatin

  • 1-1/2 tbsp water

for the swiss meringue buttercream:

• 6 egg whites (180g liquid egg whites)

• 2 cups granulated sugar

• 1-1/2 cups softened unsalted butter

• 2 tsp vanilla extract

• 1/4 tsp kosher salt

steps

for the compote:

1. In a medium saucepan on medium heat, add the berries, water, sugar, and optional lemon juice. Bring to a simmer and let it simmer ~10-15 minutes until the liquid has mostly evaporated and mixture coats a spoon (it will further thicken once cooled too). 

2. Pour into a heatproof bowl and let cool. Set aside.

for the cake:

1. Separate the egg whites and yolks into two large mixing bowls (put the egg whites into your stand mixer bowl if using one which I'd highly recommend). Set the yolks aside.

2. Whisk or beat the egg whites until frothy. Sprinkle in the sugar 1 spoonful at a time as you continue to whisk the egg whites until they reach stiff peaks.

3. Preheat the oven to 350F.

4. In the bowl with the egg yolks, add milk, oil, and vanilla extract. Mix until thoroughly combined. In a separate small mixing bowl, add the flour, cornstarch, and baking powder. Whisk until evenly mixed and then add this into the egg yolks mixture. Fold until no flour clumps remain and mixture is smooth.

5. Add 1/3 of the egg yolk-flour mixture into the egg whites mixture. Fold gently until mostly mixed. Add the rest of the egg yolk mixture in and repeat until no streaks remain.

6. Prepare your cake tins by cutting parchment paper rounds to fit the bottoms. Do not oil the tins. Divide and pour the cake batter evenly into the tins. You may use a spatula to spread it out if making thinner layers like I did. Tap the tins on the counter 2-3 times to get larger air bubbles out.

7. Bake until the tops are lightly golden brown - for ~20-25 minutes if making thinner cakes, or ~25-27 minutes if making thicker cakes.

8. Turn pans upside down on wire rack to cool without deflating. Once cooled, use a spatula or knife to run around the edge and turn out to release the cakes. If not assembling same day, gently wrap in 2 layers of plastic wrap and place in fridge until assembly.

for the whipped frosting:

1. On the day of assembly, prepare the frosting. If making the stabilized version, add the gelatin and water to a small heatproof bowl. Whisk until combined and let sit for 5 minutes.

2. To a large mixing bowl or stand mixer, add heavy whipping cream, powdered sugar, and vanilla. Whisk until soft peaks. If not stabilizing, continue to whisk to stiff peaks. I also added a couple tablespoons of my berry compote in during whisking for a light purple/blue color.

3. If stabilizing, the gelatin should've solidified by the time you've reached soft peaks. Microwave the gelatin for 5-10 seconds until liquid again but not hot. Drizzle it into the whipped cream while you continue to whisk into stiff peaks.

for the swiss meringue buttercream:

1. In a small to medium sized heatproof mixing bowl, add the egg whites and sugar. Whisk together.

2. Create a double boiler by bringing a small pot of water to a simmer. Ensure that the water level isn't too high and won't touch your mixing bowl bottom. Place your mixing bowl with the egg whites over the simmering water and continue to whisk for about 4 minutes until the mixture is thin and frothy, sugar has completely dissolved, and mixture is at 160F.

3. Do not cool the mixture - transfer it to your stand mixer bowl (preferably metal since this is hot). Use the whisk attachment to beat until soft or stiff peaks. This may take a while so I don't recommend using a hand mixer.

4. While waiting for soft or stiff peaks, cut the butter into 1 tbsp pieces.

5. The bowl should be cool to touch once you've reached soft to stiff peaks. Switch to a paddle attachment and set to medium speed. Add the softened butter in 1 tablespoon at a time, waiting for each piece to completely mix in before adding the next one. Once butter is all added, add in the vanilla and salt and continue to mix in. The frosting may look split while adding the butter, but just continue to beat the mixture and it will eventually come together.

for assembly:

1. I alternated by adding cake, whipped frosting, a few spoonfuls of compote, then repeat until all cake layers were used. Once fully stacked, I created a light crumb coating using the remaining whipped frosting outside the full cake. I transferred this to the fridge to chill for 1 hour.

2. After chilling, I applied the buttercream to the outside by piping the sides and top, then using an offset spatula and bench scraper to smooth it out. I then added a little bit of berry juice to my remaining buttercream to create a pink color, added this into a piping bag with a Wilson 32 piping tip to create the flowers.

3. I microwaved the remainder of my frozen berries to defrost them completely, strained the liquid with a sieve, and then topped my cake with the berries for an extra punch of acidity.