Take your marinade ingredients - buttermilk, chilli powder, salt, garam masala, green chillies (cut into big pieces) and mix with a whisk or fork. (If you don't have ginger-garlic paste on hand, you can make some by combining 5-6 cloves of garlic with a 1 inch knob of ginger in a food processor or by finely grating using a microplane.)
Add in your chicken pieces. I like to use wings for this recipe, but feel free to use any combination of drumsticks, thighs, breasts as well. Let it sit in the fridge overnight or for at least 6 hours.
When you're ready to fry, take your chicken out of the fridge. In a shallow bowl, add your flour and spices and combine with a whisk.
Take your chicken piece and shake off excess marinade. With one hand, dip it into the flour and make sure the entire piece is well coated. Place on a plate or rack. Continue to do this for all pieces.
Add a few pieces at a time to the oil. Fry until golden brown. If the chicken is taking a while to fry, then your oil is not hot enough. Add less chicken and raise the heat. If the chicken is frying quickly and nearly burning, lower the heat and add more chicken to the pot to help drop the temperature. The internal temp of the chicken should be 165F.