To make the process easier, I used muffin tray again instead of cake pan even though the recipe is meant for cake. I omitted the cocoa powder and in place of it, tried adding raisins to a quarter of the mixture, one whole tea bag of green tea leave (from a Japanese brand) to another quarter, one whole package of instant coffee granules to another and finally some blueberries (I happened to have just enough left in the fridge) to the last quarter.
To my utmost surprise, maybe I had too many failures previously, all 4 flavours turned out yummy. The blueberry ones were most delicious, followed by raisins (though not exciting), coffee and green tea. I think the green tea leaves were not meant for baking and therefore the taste was weaker but it was still quite delectable. It was a happy day for me.