In a small bowl, whisk together baking blend, sweetener, whey protein, baking powder, and salt. Add egg, butter, water, lemon zest, and vanilla extract and whisk until well combined. Divide batter evenly among prepared ramekins or cake pans.
Bake 20 to 22 minutes, until center of cake is set and just firm to the touch. Remove and let cool, then run a sharp knife around the inside of the ramekins or cake pans to release.
In a small bowl, beat cream cheese, butter, sweetener, and lemon zest until well combined. Add lemon juice and whipping cream and beat until smooth.
Spread the first cake layer with half of the frosting. Top with another cake layer and more frosting. Refrigerate about half an hour to set.
Serves 2 to 4. For two servings, each serving has 3.38g NET CARBS.Food energy: 319kcal Saturated fatty acids: 17.56g Monounsaturated fatty acids: 7.11g Polyunsaturated fatty acids: 1.06g Total fat: 27.06g Calories from fat: 243 Cholesterol: 79mg Carbohydrate: 10.37g Total dietary fiber: 6.69g Protein: 9.55g Erythritol: 30g