Preheat your oven to 350F. Grease an 8-inch cake pan and set it aside.

In a large bowl, mix the almond flour, egg yolks, sugar, and lemon zest thoroughly.

In another bowl, beat the egg whites until they form stiff peaks.

Gently fold the beaten egg whites into the almond flour mixture until everything is well combined.

Pour the batter into the prepared cake pan and sprinkle the sliced almonds on top if using.

Bake for 30 minutes or until the top is set and tender.

Let the cake cool in the pan for 15 minutes, then carefully invert it onto a plate.

If desired, sprinkle with powdered sugar before serving.