Lemon Layer Cake with Fluffy White Icing

Serves 10 to 12

1 cup juice from about 6 lemons
1 tsp powdered gelatin
1 1/2 cups 10 1/2 ounces sugar
1/8 tsp salt
4 large whole eggs plus 6 large egg yolks (reserve the egg whites for the cake)
8 Tbs 1 stick unsalted butter, cut into 1/2-inch cubes and frozen
1 1/4 cups 9 oz cake flour, plus extra for the pans
1 cup whole milk, at room temperature
6 large egg whites, at room temperature
2 tsp vanilla extract
1 3/4 cups 12 1/4 oz sugar
4 tsp baking powder
1 tsp salt
12 Tbs 1 1/2 sticks unsalted butter, cut into 12 pieces, softened but still cool
1 cup 7 oz sugar
2 large egg whites, at room temperature
1/4 cup water
1 Tbs juice from 1 lemon
1 Tbs corn syrup

For the Filling

Measure 1 tablespoon of the lemon juice into a small bowl.

Sprinkle the gelatin over the top.

Heat the remaining lemon juice, the sugar, and salt in a medium saucepan over medium-high heat, stirring occasionally, until the sugar dissolves and the mixture is hot but not boiling.

Whisk the eggs and yolks in a large bowl.

Whisking constantly, slowly pour the hot lemon-sugar mixture into the eggs, then return the mixture to the saucepan.

Cook over medium-low heat, stirring constantly with a heat proof spatula, until the mixture registers 170°F on an instant-read thermometer and is thick enough to leave a trail when the spatula is scraped along the pan bottom, 4 to 6 minutes.

Immediately remove the pan from the heat and stir in the gelatin mixture until dissolved.

Stir in the frozen butter until incorporated.

Pour the filling through a fine-mesh strainer into a bowl (you should have 3 cups).

Lay a sheet of plastic wrap directly on the surface a refrigerate until firm enough to spread, at least 4 hours.

For the Cake

Adjust an oven rack to the middle position and heat the oven to 350°F.

Grease and flour two 9-inch-wide by 2-inch-tall round cake pans and line with parchment paper.

In a 2-cup liquid measure or a medium bowl, whisk together the milk, egg whites, and vanilla.

In a stand mixer fitted with the paddle attachment, mix the flour, sugar, baking powder, and salt at low speed until combined, about 30 seconds.

With the mixer running at low speed, add the butter once piece at a time; continue beating until the mixture resembles moist crumbs with no visible butter chunks.

Add all but 1/2 cup of the milk mixture to the crumbs and beat at medium speed until the mixture is pale and fluffy, about 1 1/2 minutes.

With the mixer running at low speed, add the remaining 1/2 cup of the milk mixture; increase the speed to medium and beat for 30 seconds more.

Stop the mixer and scrape the sides of the bowl.

Return the mixer to medium speed and beat for 20 seconds longer.

Divide the batter evenly between the pans, smoothing the tops with a rubber spatula.

Lightly tap the pan against the countertop two or three times to settle the batter.

Bake until a toothpick inserted in the center of the cakes comes out clean, 23 to 25 minutes, rotating pans halfway through the baking time.

Cool the cakes in the pans on a wire rack for 10 minutes.

Run a small knife around the edges of the cakes, then flip them out onto a wire rack.

Peel off the parchment paper, flip the cakes right side up, and cool completely before frosting, about 2 hours.

To Assemble

Line the edges of a cake platter with strips of parchment paper to keep the platter clean while you assemble the cake.

Use a serrated knife to cut each cake horizontally into two even layers.

Place the bottom layer of one cake on the platter.

Using a spatula, spread 1 cup of the lemon filling evenly on the cake, leaving a 1/2-inch border around the edge.

Carefully place the upper cake layer on top of the filling.

Spread 1 cup of the filling on top; repeat using the remaining filling and cake layers.

Smooth out any filling that has leaked from the sides of the cake.

Cover with plastic wrap and refrigerate while making the icing.

For the Icing

Combine all the ingredients in the bowl of a stand mixer or a large heatproof bowl and set over a medium saucepan filled with 1 inch of barely simmering water (do not let the bowl touch the water).

Cook, stirring constantly, until the mixture registers 160°F on an instant-read thermometer, 5 to 10 minutes.

Remove the bowl from the heat and transfer the mixture to a stand mixer fitted with the whisk attachment.

Beat on medium speed until soft peaks form, about 5 minutes.

Increase the speed to medium high and continue to beat until the mixture has cooled to room temperature and stiff peaks form, 5 minutes longer.

Using a spatula, spread the frosting evenly over the top and sides of the cake.

Remove the parchment strips from the platter and serve.

The Complete America's Test Kitchen TV Show Cookbook 2001-2017. Pages 746-748. U.S.A.: Penguin Random House, 2016.