Blueberry Lemon Layer Cake

Preparation

1. Make the cake: 

   1. Step 1

      Heat the oven to 350 degrees. Lightly coat three 8-inch cake pans (see Tip) with cooking spray and then line the bottoms with rounds of parchment paper. Set aside.

   2. Step 2

      Add the granulated sugar and lemon zest to the bowl of a stand mixer with the paddle attachment (or you can use a large bowl with a hand mixer). Use your fingertips to rub the mixture together—this will help enhance the lemon flavor by extracting the fragrant oils into the sugar. Add the butter and vanilla extract. Beat on medium speed until light and fluffy, 2 to 3 minutes. Pour in the oil and mix until just combined. Crack in the eggs and beat until very smooth, about 1 minute, scraping down the sides and re-mixing, if necessary.

   3. Step 3

      In a medium bowl, whisk together the flour, baking powder and salt. In a small measuring cup, combine the milk and lemon juice (the milk may curdle a bit, but that’s fine!).

   4. Step 4

      To the bowl of the butter mixture, add half of the dry ingredients and half of the milk mixture. Mix on low speed until combined. Add the remaining dry ingredients and milk mixture and mix one last time, scraping down the sides of the bowl. Fold in the 2 cups blueberries. 

   5. Step 5

      Divide the batter between the prepared baking pans. (It should be about 460 grams for each pan.) Transfer the pans to the oven to bake for 20 to 22 minutes, rotating them halfway through, until a skewer inserted into the center comes out clean.

   6. Step 6

      Let cakes cool for 15 minutes on cooling racks, then invert onto racks, peel off parchment and let cakes cool completely. (If desired, you can wrap the cooled cakes in plastic wrap and refrigerate them for up to 1 day before frosting.)

2. Start the frosting: 

   1. Step 7

      Place a sieve or fine-mesh strainer over a small or medium bowl (you’ll use it to strain the blueberry sauce later). In a small bowl, mix the cornstarch with 1 tablespoon water and set aside.

   2. Step 8

      In a small saucepan, combine 1½ cups blueberries, the granulated sugar and 1 tablespoon water. Place over medium-low heat and cook for 4 to 6 minutes, until the sugar dissolves and the mixture is bubbling, mashing the berries with a large spoon to help them break down.

   3. Step 9

      Stir in the cornstarch slurry and cook until the mixture starts to bubble and thicken, about 2 minutes, then cook for 1 minute more. Remove from the heat and strain the blueberry sauce through the sieve into the bowl, making sure to scrape any extra from the bottom of the strainer once you’re done. (Measure out ½ cup of blueberry sauce; if you like, save any remaining blueberry sauce to stir into your morning iced latte.) Place a layer of plastic wrap directly on the surface of the sauce and let it cool to room temperature along with the cakes; this should take about 1 hour. (The goal here is to have the sauce be the same temperature as the butter for the frosting to guarantee the frosting doesn’t break.)

3. Finish the frosting:

   1. Step 10

      Once the blueberry sauce has cooled, proceed with the frosting. In a stand mixer using the paddle attachment (or a hand mixer), beat the butter with the vanilla and salt on medium speed for 1 minute, until light and fluffy. Scrape down the sides of the bowl. Add about 1 cup of the powdered sugar, mixing on low speed until combined. (If you plan to add piped decorations, set aside some frosting at this point; see Tip.) Add the ½ cup of blueberry sauce and mix until combined.

   2. Step 11

      Scrape down the sides of the bowl, then add the remaining powdered sugar a little at a time with the mixer on low speed. Once all the powdered sugar has been added, scrape down the sides and bottom of the bowl, adjust the mixer to medium-high speed and beat the frosting for a full minute, until everything is combined and the frosting is light and fluffy.

4. Assemble the layer cake:

   1. Step 12

      If any of the cooled cakes have domed tops, feel free to level them with a serrated knife to make three even, flat layers. To assemble, place one cake layer on a serving plate or cake stand (see Tip) and use an offset spatula to spread the top evenly with about ⅔ cup of the frosting. Repeat with the second cake layer and another ⅔ cup of frosting, then top with the third cake layer.

   2. Step 13

      Apply a “crumb coat” to the cake: Use ½ cup frosting to apply a thin, even coat of frosting to the outside of the cake, then transfer to the fridge to chill for 20 minutes (this will firm up the frosting). Once the crumb coat has set, spread the remaining buttercream (about 2 cups) over the cake and decorate if desired with any remaining blueberries. (To add piped decorations, see Tip.) 

   3. Step 14

      You can serve it right away, but for the cleanest cuts, refrigerate the cake for at least an hour (or up to 4 hours). If storing for longer, lightly cover the outside with plastic wrap to prevent the buttercream from drying out. Bring the cake to room temperature again before serving.