Lemon Sheet Cake with Lemon Buttercream Frosting
A bright yellow lemon cake demands a place at your Easter holiday table, particularly this one. Every element – from cake to syrup to buttercream – is infused with lemon flavor. If you’d prefer a less tart cake, you can dial back the lemon juice in the buttercream and leave it out altogether in the syrup – the cake will still be lovely, but just a tad less pucker-inducing.
For the cake:
- 2 cups cake flour, sifted (250 g)
- 1 cup all purpose flour (135 g)
- 2 tsp baking powder
- 3/4 tsp salt
- 2 cups granulated sugar (400 g)
- 1/4 cup packed(ish) lemon zest (20 g)
- 2 sticks unsalted butter, room temperature (226 g)
- 1 tsp lemon extract
- 1/2 tsp pure lemon extract
- 3 large eggs
- 1 yolk
- 1/4 cup lemon juice
- 1 cup sour cream (215 g)
For the lemon simple syrup:
- 1/4 cup water
- 1/4 cup granulated sugar (50 g)
- 1 tbsp freshly-squeezed lemon juice
For the frosting:
- 3 sticks unsalted butter, softened (339 g)
- 1 1/2 tbsp lemon zest
- 1/4 tsp table salt rounded
- 6 cups confectioners' sugar, sifted if lumpy (600 g)
- 3/4 cup freshly-squeezed lemon juice or to taste
- A few drops of yellow gel food coloring
- Yellow sparkling sugar
- Preheat the oven to 350-degrees. Grease a 13x9x2-in pan with softened butter or cooking spray. Line the bottom with parchment paper and grease again. Set aside.
- In a medium-sized bowl, whisk together the flours, baking powder, baking soda, and salt and set aside.
- In the bowl of a stand mixer, fitted with the paddle attachment, combine the sugar and the zest and using your fingers, rub the zest into the sugar until fully incorporated. Add the butter and extracts and beat on medium-medium high speed, until light and fluffy, about 3 to 5 minutes, scraping down the bowl with a rubber spatula as needed. On low speed, add the eggs and yolk, one at a time.
- Combine the lemon juice and sour cream in a small bowl. Add the dry ingredients to the stand mixer in three installments, alternating with the juice/sour cream, and beginning and ending with the dry. Stop the mixer when you still see a few streaks of flour and finish mixing by hand.
- Transfer the batter to the prepared pan, smooth the top, and bake for 30 to 35 minutes, rotating at the halfway point, until a toothpick inserted in the center comes out with a moist crumb or two.
- Meanwhile, make the simple syrup, heat the water and sugar on the stovetop on medium heat until the sugar melts. Off of the heat, add the juice, stir to combine, and let come to room temperature.
- Let the cake cool on a rack for 10 to 15 minutes before inverting the cake right side up. Once at room temperature, poke the cake all over the top with a toothpick and brush the cake with the simple syrup.
- To make the buttercream, beat the butter and zest on medium speed, in the bowl of a stand mixer, fitted with the paddle attachment, until softened and smooth. Add the salt and then the sugar, a cup at a time, alternating with the lemon juice, and beating thoroughly between each addition.
- Continue beating about 3 to 5 minutes more, until light and fluffy. Add the yellow food coloring and beat a final time to combine.
- Spread the frosting over the cooled cake in large swoopy swirls and sprinkle with the yellow sparkling sugar. The cake will keep on the counter, tightly wrapped in plastic wrap for up to 3 days.