Sieve together wheat flour, baking soda and baking powder. Set aside.
Take mixed raisins and add 1/2 tsp flour to it. Mix well and set aside.
Line a muffin pan with paper liners and set aside.
Preheat oven at 180 degree.
In a mixing bowl, take sugar and oil. Mix both till sugar melts. Add curd and mix well. Add milk and vanilla essence and mix again.
Take banana in a separate bowl and mash it with the help of a fork. Add it to the oil mix and whisk everything well.
Add flour mix little by little to the oil banana mix. Whisk well to make a lump-free batter. The batter should not be too thick or too watery. If you find that the batter is too thick add one more tbsp milk.
Finally add raisins to the batter and give it a stir. Take the chocolate bar and cut it into six equal pieces.
Take the prepared batter and fill the muffin cups till 1/4. Put a piece of chocolate in the center and top it up with some more batter. Do not fill the cups more than half. Likewise, fill all the muffin cups with a piece of chocolate in.
Bake the muffins for 20 minutes or till a knife inserted comes out clean. Take out the tray from the oven and let the muffins rest for 3-4 minutes.
Remove the muffins from the tray. Let them cool on a wire rack.