Preheat your oven to 150C/ 300 F and line a 20 cm/8″ springform pan with parchment paper. Place your Keto marzipan in a bowl, and break it up into smaller pieces. It is easier if your marzipan is at room temperature, so you can microwave it for a few seconds to warm it up.
Crack the eggs, and separate the whites from the yolks. Add the whites to a bowl of a stand mixer and beat until stiff peaks form, for around 5-7 minutes. You can also whip the egg whites in a glass bowl using a hand mixer.
To the bowl with the marzipan, add 1 egg yolk and mix using a fork. Repeat with the remaining egg yolks. Combining the marzipan and egg yolk will be hard at first, but it will get easier as the mixture loosens up.
Add a third of the whipped egg whites to the marzipan mixture. Whisk to combine and further loosen the mixture. Add the remaining egg whites.
Gently fold the whites into the marzipan mixture. Don’t whisk, or else you will knock off the air from the batter. Stop folding when most of the whites are folded in; it’s okay to have a few white spots.
Pour the cake batter into the lined pan. Spread it using a spoon or spatula. Transfer the pan to the oven to bake.
Bake for 10 minutes at 150 C/300 F then, reduce the heat to 120 C/ 250 F and bake for another 20-25 minutes. The cake should be golden when done, and an inserted toothpick should come out dry.
Take the cake out of the pan and place it on a serving platter. Let it cool completely. Once it’s no longer hot, you can garnish it with powdered sweetener dusting.
Cut the cake into 8 equal slices. You can add sugar-free frosting or icing to the top. Serve immediately.