Ingredients

Cake:

1 cup (2 sticks) unsalted butter, room temperature, plus more for pans

2 ½ cups all-purpose flour (spooned and leveled), plus more for pans

½ teaspoon baking powder

½ teaspoon baking soda

1 teaspoon salt

1 tablespoon lemon zest

2 cups sugar

2 large eggs plus 3 large egg yolks

¼ cup plus 2 tablespoons fresh lemon juice

1 cup low-fat buttermilk

1 lemon, thinly sliced and seeded

Frosting:

3 large egg whites

¾ cup sugar

Pinch of salt

1/3 cup water

2 tablespoon lemon juice

Preparation

Cake:

  1. Preheat oven to 350 degrees. Butter and flour two 8-by-2-inch cake pans, tapping out excess flour. In a medium bowl, whisk flour, baking powder, baking soda, salt, and lemon zest.

  2. In a large bowl, using an electric mixer, beat butter and 1 ½ cups sugar until light and fluffy. With mixer on low, beat in eggs and yolks, one at a time. Beat in 2 tablespoons lemon juice. Alternately beat in flour mixture and buttermilk beginning and ending with flour mixture; mix just until combined.

  3. Divide batter between pans; smooth tops. Bake until cakes pull away from sides of pans, 32 to 35 minutes. Let cool in pans 10 minutes. Run a knife around edges of pans and invert cakes onto a wire rack.

  4. While cakes are baking, bring remaining ½ cup sugar and ½ cup water to a boil in a saucepan. Add lemon slices and simmer 25 minutes. Using a slotted spoon, transfer lemon slices to a waxed-paper-lined plate. Stir remaining ¼ cup fresh lemon juice into syrup.

  5. Using a toothpick, poke holes in warm cakes on rack. Brush with lemon syrup. Let cool completely. Prepare frosting, substituting 2 tablespoons fresh lemon juice for vanilla extract. Frost cooled cakes and top with candied lemon slices.

Frosting:

  1. In a heatproof bowl set over (not in) a saucepan of simmering water, combine 3 large egg whites, ¾ cup sugar, a pinch salt and 1/3 cup water. Cook over medium, stirring constantly, until sugar has dissolved (or mixture registers 150 on an instant-read thermometer), 2 to 3 minutes. Transfer to a large bowl. Using an electric mixer, beat on medium-high until glossy, stiff peaks form (do not overbeat), about 3 minutes; reduce speed to low, add lemon juice, and beat just until combined. Use immediately.