Separate the eggs, placing yolks in one bowl and whites in another.
Whisk the egg yolks with the sugar until pale and creamy.
Add the drained ricotta, softened butter, vanilla, and lemon zest to the yolk mixture and mix until smooth and the color becames lighter.
Fold in the almond flour until fully combined.
In a separate bowl, using cleaned and dried whisks, whip the egg whites until stiff peaks form.
Gently fold the whipped egg whites into the batter, using a bottom-to-top motion with a spatula, keeping it airy.
Grease an 8-inch (20 cm) cake pan and line the base and sides with parchment paper.
Pour in the batter, smooth the top, and sprinkle with almond flakes.
Bake at 350°F (180°C) for about 50 minutes or until golden and set in the center.
Let cool in the pan for 10 minutes before transferring to a rack to cool completely. Slice and enjoy!
