To make the spicy marinade, mix the yoghurt, buttermilk, chilli powder, turmeric, green chillies and coriander together in a bowl. Turn the chicken thighs in the marinade so it is coated, cover and leave in the refrigerator for about 2 hours.
To make the pickled mooli, steep the sliced mooli in the pickling liquor for 1–2 hours at room temperature, then keep in the refrigerator until needed.
Pour the vegetable oil in a deep frying pan (skillet) or kadai, and heat until it is about 180°C (350°F). The oil is hot enough when a cube of bread sizzles when dropped into it. While the oil heats up, combine the flour, cornflour, chilli powder and turmeric in a shallow bowl.
Lift the chicken out of the marinade and coat in the flour-mix, shaking off any excess. Deep-fry in the oil for about 5 minutes until the outside is golden brown. To ensure the chicken is cooked through, test the middle of the biggest piece of chicken with a probe thermometer; it should be over 75ºC (167ºF).
Remove the chicken from the fryer and drain on kitchen paper. Sprinkle generously with chaat masala. Serve with the pickled mooli, fried curry leaves and the curry leaf mayonnaise.