Preheat the oven to 350ºF and lightly grease 4 (four) 8-ounce ramekins. Set the ramekins in a larger baking dish.
In a large bowl, beat the sweetener and butter together until well combined. Beat in the egg yolks one at a time, then beat in the almond flour, lemon zest, and salt.
Stir in the lemon juice and cream. Set this mixture aside.
In another large bowl, using clean beaters, beat the egg whites with the cream of tartar until they hold very stiff peaks.
Gently fold the two mixtures together, taking care not to deflate the egg whites. Divide between the prepared ramekins and fill the baking dish with hot water until it reaches about halfway up the ramekins.
Bake 35 to 40 minutes, until the cakes are puffed up and light golden brown but still have a little bit of jiggle in the center.
Remove the ramekins from the baking dish immediately and let cool 15 minutes, then dust with powdered sweetener and enjoy warm.