Wash the urad dall in cold water and soak it over night. Once soaked, transfer it to a blender and add 2 cups of old water, the green chilies, and ginger and grind the mixture until it is a lovely grainy texture.
Transfer te dall mixture to a mixing bowl and add the soda bicarbonate and mix well. Take a tablespoon of the hot oil from the wok and add it to the mixture. Adding the soda bicarbonate and the hot oil to the dall mixture will make the vadas soft and fluffy. I learnt this from my father in law.
Check that the oil is hot by dropping a small piece of the dall mixture into the oil. If it comes up too fast – the oil is ready. Reduce the heat and using a spoon or your hands, drop some of the dall mixture into the oil. I made mine quite small to ensure that the vadas get cooked well. the vadas float up when they cook, turn them and once they are all golden brown, remove them.
Once all the vadas are cooked, boil a kettle of water and pour it in a mixing bowl. Add the fried vadas to it and allow them to soak up the water. The vadas will puff up when they soak up the water.
In another mixing bowl, transfer the Greek style yogurt and whisk it using a hand whisk. Add some salt to taste.
Remove the vadas from the water and gently squeeze and flatten them using your palms and transfer them into the yogurt. once all the vadas are added to the yogurt - allow them to soak up the yogurt. Garnish the top by sprinkling the ground cumin and chili powder and some chopped coriander. Leave these to cool in the fridge for as long as possible. You will find that when you are ready to serve the vadas, your yogurt mixture will be a lot thinner than it was and that's normal.
Serve the dahi vadas in individual bowls and garnish them with the dates and tamarind chutney and the green coriander and chili chutney. My family loves them with hot and spicy chili chutney with a hint of the sweet and sour tamarind chutney.