Preheat oven to 180C
Cut the melon fruit in pieces. Discard the seeds.
In a pan directly add the watermelon pieces and cook on medium flame by stirring continuously.
In 5-10 minutes the water will start to evaporate and form a thick fruit pulp.
Let it cool a little and grind it into smooth liquid.
Sieve flour baking soda baking powder salt
Whisk together watermelon pulp buttermilk and sugar
Mix flour mixture in wet mixture in 2-3 portions.
Wheat flour absorbs lot of liquid. If you find batter to be very thick then adjust by adding some milk or water or buttermilk.
Scoop in the cup cake liners till 3/4 full, Sprinkle some choco chips on top.
Bake for 15-20 minutes on 180C. Or until toothpick inserted comes out clean.
Everything used should be on room temperature.
Also overbeating and very liquidy batter leads to a bad cake which can be undercooked from the centre or sink when cooled.