Start by ensuring that your mixing bowl and beaters are completely clean and free from any grease. Set the oven to preheat at 325°F (163°C).

In a large mixing bowl, use an electric mixer on high speed to beat the egg whites along with the cream of tartar until stiff peaks form, about 3 to 5 minutes.

In another bowl, combine the softened cream cheese, powdered erythritol, vanilla extract, and a pinch of salt. Blend on medium speed until smooth and creamy, about 2 to 3 minutes.

Gently fold the whipped egg whites into the cream cheese mixture using a spatula, preserving the airy texture.

Pour the cake batter into a prepared 9-inch round cake pan and smooth the top evenly.

Bake at 325°F (163°C) for approximately 30 minutes, until lightly golden and a toothpick comes out clean.

Cool the cake in the pan for about 15 minutes, then transfer it to a wire rack to cool completely.