Measure half of these ingredients.

Butter and dust with flour, an 8 inch round pan. You can also fill it in muffin cups (reduce the cooking time to half if doing so)

Mix together flour, baking powder, soda and salt together. Sift and keep aside.

Beat sugar and butter until light and fluffly.

Add eggs and egg whites one by one and beat well.

Add flour mixture and sour cream alternately and fold until well incorporated.

If you do no have a leftover chocolate batter, you can divide the complete batter (without halving ingredients) into two. Add about 50 gms of cocoa powder to one and keep the other as is.

Add the vanilla base to the pan. Add the chocolate batter on top and give a swirl any which way you like :)

Bake in a preheated oven (180 degrees) for about 30 mins. Do check at 20 min to see if it is cooked, as cooking time might differ in your oven. A toothpick inserted should come out clean.