Preheat your oven and prepare a 9-inch cake pan by lining the bottom with parchment paper — this prevents sticking and keeps the cake’s tender bottom intact. In a large mixing bowl, whisk together your egg yolks, melted and cooled butter, vanilla extract, powdered keto sweetener, almond flour, baking powder, and salt. Stir until smooth and evenly combined; a few small clumps may remain, but don’t overmix. The yolk mixture forms the rich, flavorful base of the cake.

In a separate, clean bowl, add the egg whites and cream of tartar. Use an electric mixer to whip until stiff peaks form — this means the whites should stand tall without collapsing when you lift the beaters. The whipped egg whites are essential for giving the Cloud Cake its signature airy lift, so don’t rush this step. The texture should be glossy and firm before you proceed.

Gently fold about one-third of the whipped egg whites into the egg yolk mixture using a rubber spatula. Folding should be slow and deliberate to preserve as much air as possible. Once that portion is incorporated, fold in the remaining whipped whites in batches until no white streaks remain. Take your time — this delicate folding is what gives your cake its fluffy, cloud-like crumb.

Pour the batter into the prepared cake pan and smooth the top with a spatula. Place in the preheated oven and bake until the cake rises beautifully and turns golden on top, with a springy texture when gently touched. Remove from the oven and let it cool completely before unmolding. You can serve it plain, sprinkle with a little extra powdered sweetener, or add whipped cream and berries for an elegant touch.