Pre-heat oven to 180°C (356°F).
Make the frosting by mixing the yogurt, cocoa powder and 0 calorie icing sugar together until smooth. Set aside in the fridge.
Using an electric hand whisk, beat together the egg and stevia on high until light and fluffy, about 3-5 minutes.
Mix in the yogurt and then fold in the flour, cocoa powder and baking powder until well combined.
Transfer the batter to a 5-inch cake tin and bake for 15-18 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool before frosting. Cut the cake into 4 slices, serve and enjoy!