To begin with pre heat your oven at 180C /350F for 10 minutes.
Meanwhile take muffin molds or prepare your muffins tray by placing muffin liners in cavities.
Now mix all the wet ingredients like curd, oil, sugar and vanilla extract. Whisk it well.
In a separate bowl add dry ingredients - all purpose flour, baking soda and baking powder. Whisk to combine.
After that pour wet ingredients onto dry ingredients and combine well. Scoop out 2-3 tbsp of muffin batter into a separate bowl.
To this bowl add cocoa powder and mix well. Add in hot water to adjust the consistency.
We shall be using this to create swirls to have the marble effect. You should now have two batters, one vanilla and other chocolate.
Now first pour vanilla batter till 1/2 in all the liners with a spoon, then make 3 round swirls on top using a piping bag. Take a tooth-pick and create a marble effect as shown in the picture.
Bake these muffins in a pre heated oven at 150°C for 22-25 minutes. Once baked cool on rack and enjoy.