First of all, wash the drumsticks and drain well. Now in a big mixing bowl, whisk the yogurt to smooth and add 2 cup of water and 1/4 teaspoon of salt to it and mix well. Soak the drumstick in this and cover the bowl with cling film. Keep the bowl in fridge for at least an hour. You can keep them soaked for more time, this will tenderise chicken more.
After that, drain them completely and with the help of knife, scrape all the meat towards the head of drumsticks to give them lollipop shape.
Add 1 tablespoon of ginger garlic paste, 1/2 teaspoon salt, black pepper powder, 1/4 teaspoon chilli powder, corn flour and all purpose flour to the drumsticks and mix them well so that they are nicely coated.
Heat sufficient oil in a kadhai/pan for deep frying over medium-high heat. Shape all the drumstick heads round and deep fry them 3-4 drumsticks at a time,until they are cooked properly and are nice golden brown in colour.
Take them out and put them on a plate with kitchen towel.
Now in a wide pan, add 2 tablespoon oil from the hot oil. Add chopped onion and saute for a minute. Add 1 tablespoon ginger garlic paste and saute again till the raw smell fades.
Add chilli sauce, soya sauce, vinegar, salt, red chilli powder to it and saute again. Now add 1/2 cup of water and bring the mixture to boil. Add sugar and mix well. Let the sauce cook and thickens a little.
Add fried chicken pieces now and toss them in the mixture so that they are well coated. Switch off the heat.
Garnish with chopped spring onions and cover the bone part of drumsticks with foil for easy pickup.
Serve Hot and Enjoy.