Preheat oven to 325 degrees Fahrenheit.

In a medium bowl, whisk together flour and baking powder.

In a large bowl, beat egg whites until frothy using a mixer.

Add cream of tartar to the egg whites and continue beating until stiff peaks form.

Gradually sprinkle sugar and sugar substitute over the egg whites, gently blending until combined.

Add vanilla extract to the egg white mixture and stir to combine.

With a hand mixer on low speed, slowly sprinkle the flour mixture into the egg mixture, about 1 tablespoon at a time, mixing after each addition.

Ensure the flour is fully incorporated into the batter.

Pour the batter into a medium cake pan or individual cupcake papers.

Bake until the top springs back when lightly poked, approximately 25 minutes.

Remove from oven and let cool before serving.