Take yogurt in a bowl and add salt, black salt and roasted cumin powder. Beat it using a whisk until yogurt is smooth and spices are mixed well.
Add red chili powder to the center and keep the bowl aside. DO NOT MIX the chili powder in the yogurt. We are going to add hot tempering on the chili powder.
Heat the oil in a small tadka pan. Once hot add cumin seeds and let them sizzle a bit.
Add ginger, green chili and curry leaves. Saute for 40-50 seconds or until the raw smell of ginger goes away.
Pour this tempering immediately on top of the chili powder.
Mix it with a spoon and it is ready to serve.
Notes
Raita tastes best when served chilled. So always use chilled yogurt from the refrigerator. Or make plain raita ahead of time and chill for a few hours before serving.