Preheat oven to 350 degrees F for 5 minutes Grease and flour a baking tin.
Mix the flour, baking powder, and baking soda together by passing them through a sieve a couple of times.
Beat the eggs with a mixer until pale and smooth, add erythritol, stevia and vanilla extract to the mix. Add the dry ingredients with melted butter, milk and mix well.
Distribute the cake batter equally in 2 containers, add cocoa powder to one of the batter and mix well.
Pour the batter alternately into the baking tin,make couple of swirls with a butter knife, bake 40 to 45 minutes or until toothpick comes out clean. Cool on wire racks for 10 minutes. Cut the cake in slices and serve.
Notes
Substitute erythritol/stevia with ¾ cup brown sugar if you want to make it the standard way.
You may use ¾ cup of wholemeal four with 1 cup plain flour to make a more healthy version of the cake.