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Lemon Blackberry Cake

Two layers of plush lemon cake studded with fresh blackberries and sandwiched between two layers of an italian meringue buttercream made with fresh blackberry puree.
Prep Time 1 hour
Cook Time 30 minutes
Servings 16 square slices

Equipment

  • 2 8 inch square cake pans

Ingredients

Lemon Cake with Blackberries

  • 250g or 1 ¼ cups fine granulated sugar
  • Zest of 3-4 lemons
  • 226g or 1 cup unsalted butter at room temperature
  • 3 large eggs at room temperature
  • 1 teaspoon pure vanilla extract
  • ½ teaspoon fine sea salt
  • 260g or 2 cups cake flour
  • 2 ¼ teaspoons baking powder
  • 120g or ½ cup full fat sour cream
  • 60g or ¼ cup freshly squeezed lemon juice
  • About 510g or 18 oz fresh blackberries some for the cake, 200g for the puree (below) and some leftover to decorate

Blackberry Meringue Buttercream

  • 200g fresh blackberries about two cups, to process into 80g or ⅓ cup blackberry puree
  • 200g or 1 cup fine granulated sugar
  • 3 egg whites from 3 large eggs - no yolk mixed in at all
  • ¼ teaspoon cream of tartar to stabilize the meringue
  • ¼ teaspoon fine sea salt or more to taste
  • 1 teaspoon pure vanilla extract
  • 254g or 1 cup plus 2 tablespoons butter unsalted and at room temperature (if using salted butter, you may want to skip adding the salt)

Instructions

Make the cake

  • Important: have your butter at a warm room temperature and your eggs at room temperature. For the eggs, you can place them in a bowl of hot water to warm them.
  • Grease and flour two 8 inch square (round works too) light colored metal pans. Preheat the oven to 350 F.
  • Into the bowl of a stand mixer, add the sugar. Zest the lemons over the sugar then use your fingers to rub the zest into the sugar to release the oils.
  • Add the butter, salt and vanilla and affix the paddle attachment. Turn the speed to medium and beat until creamed, about 3-5 minutes.
  • With the mixer on, and one by one, add the eggs. Allow 30 seconds between each egg addition. Once all three eggs are in, mix on medium speed until light and airy. (If the batter splits at this point, scroll above to read what to do).
  • Sift in the cake flour and add the baking powder. With the mixer on low, add the sour cream and fresh lemon juice. Mix until just combined - scraping down the bowl as needed to ensure an even mix.
  • Divide the batter between the two prepared pans, smooth the batter into an even layer. Arrange the blackberries on top, 16 berries per pan in rows of four (adding them on top means there will be slight sinking in the top of the cake, but adding them into the cake would have them all sinking to the bottom which we want to avoid).
  • Bake the cakes until the tops spring back when pressed in the middle (of the cake, not the berry), or a cake tester comes out clean, about 15-18 minutes.
  • Once the cakes cool slightly, carefully flip them over to release and transfer to a cooling rack to cool completely.

Make the buttercream

  • Add 200g of blackberries to a food processor and process until pureed. Press the berries through a fine mesh sieve to remove the seeds. We’ll want about 80g or ⅓ cup of blackberry juice for the syrup. You may end up with more than needed, depending on how juicy the blackberries are.
  • In a pot, add the sugar and 80g of blackberry juice, stir to combine and set over medium heat. Cook as the sugar dissolves and the mix begins to boil. Keep a thermometer handy, we’ll take it off the heat when it reaches 245 F (a little above is ok, don’t let it get over 250 F).
  • When the syrup is close to being done, add the egg whites to a clean and dry stand mixer bowl. Affix the whisk attachment and add the cream of tartar. Turn the mixer on low, whipping until the egg whites are frothy.
  • Once the sugar reaches 245 F, remove it from the heat and with the mixer on low slowly pour it onto the frothy egg whites. Scrape the pan to ensure all the syrup is in the bowl and turn the mixer to medium speed. If you see lots of syrup stuck to the sides of the bowl, stop the mixer and scrape it into the middle then continue whisking.
  • Whisk until you have stiff peaks, the meringue should hold shape when the whisk is turned upside down. Add the salt and vanilla and whisk on low.
  • Slowly add the butter, one tablespoon or pat at a time. The buttercream will split and look soupy, continue adding the buttercream. Once it’s all in, keep whisking until the buttercream is thickened and smooth (if it does not thicken, see above section on troubleshooting for what to do).

Assemble the cake

  • Lay one cake onto a serving plate and spread half the buttercream on top. Place the other cake on top, and spread the rest of the buttercream over it. Decorate with fresh berries and/or edible flowers.
  • Cake is best day of but leftovers can be stored in the fridge. Allow them to come to room temperature so the buttercream will soften before eating.

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