Step 1

Arrange a rack in the middle of the oven and heat the oven to 350°F. Line the bottom of an 8- or 9-inch springform or round cake pan with parchment paper. Coat the paper and sides of the pan well with butter or cooking spray; set aside.

Step 2

Crack and separate 4 large eggs, placing the egg whites in the bowl of a stand mixer fitted with the whisk attachment (alternatively, place in a medium bowl to and use an electric hand mixer or sturdy whisk) and the yolks in a large bowl.

Step 3

Finely grate the zest of 2 medium lemons with a Microplane to get 2 tablespoons and place in the bowl with the egg yolks. Add 1/2 cup granulated sugar and stir with a wooden spoon or sturdy rubber spatula until well-combined and no streaks of egg yolk remain.

Step 4

Add 1 1/2 cups almond flour, 1 teaspoon baking powder, and 1/2 teaspoon kosher salt. Stir until the almond flour is moistened and the mixture is just combined (some lumps are fine).

Step 5

Beat the egg whites on medium-high speed until stiff peaks form, 2 to 3 minutes (about 5 minutes by hand). Stir 1/3 of the beaten egg whites into the batter to lighten it. Then gently fold the remaining egg whites in the until just combined. The batter should be evenly moistened with no streak of egg whites remaining but will not be completely smooth; do not overmix. Transfer the batter to the prepared pan and gently spread out to an even layer.

Step 6

Bake until the edges of the cake have begun to pull away from the sides of the pan, the top is golden brown, and a toothpick inserted into the center comes out clean, 25 to 30 minutes. Place the pan on a wire rack and let cool for 15 minutes.

Step 7

To serve, run a knife around the cake to loosen it. Release the sides of the pan, if using a springform pan. If using a cake pan, flip the cake onto a plate, peel away the parchment, then flip it again onto a serving plate. Serve warm or at room temperature, dusting with powdered sugar and served with fresh berries, if desired.