Prep equipment: Preheat the oven to 350 degrees F. Place a round of parchment paper on the bottom of an 8 or 9-inch cake pan or springform pan. Lightly grease the paper and sides of the pan with oil and set it aside.
Separate the eggs: Separate the egg yolks and whites, placing the egg whites in a large bowl and the egg yolks in a separate mixing bowl.
Whisk wet ingredients: In the bowl with the egg yolks, add the maple syrup, vanilla extract, and almond extract, if using, and whisk until smooth.
Make the batter: In a separate bowl, whisk together the almond flour, cornstarch, and baking powder. Fold into the egg yolk mixture, along with the lemon zest. The batter will be thick.
Whip egg whites: To the bowl of egg whites, add the lemon juice and salt. Beat with the whisk attachment or hand mixer on medium-high speed until soft peaks form, about 2-3 minutes.
Lighten up the batter: Stir ⅓ of the beaten egg whites into the batter to lighten it. Then, gently fold the remaining egg whites in with a rubber spatula until just combined. The batter should be evenly moistened with no streak of egg whites remaining, but it will not be completely smooth. Do not overmix. Transfer the batter to the prepared pan and gently spread it into an even layer.
Bake: Bake for 25-30 minutes, or until the edges of the cake have begun to pull away from the pan, the top is golden brown, and a toothpick inserted into the center comes out clean. Place the pan on a wire rack and let cool for 15 minutes
To serve, run a knife around the cake to loosen it. If using a springform pan, release the sides of the pan. If using a cake pan, gently flip the cake onto a plate, peel away the parchment, then flip it back over onto a serving plate. Serve warm or at room temperature, topped with whipped cream and berries, if desired.