Wash urad dal,ChanaDal a few times and soak for at least 4 to 6 hours. Drain Dal.

Drain dal and add it to a blender jar.
Blend coarsely first, then pour 1 tbsp chilled water and grind it again. Scraping the sides, repeat blending adding 1 tbsp water each time only as needed until the batter turns fluffy and light. Add cumin, salt, red chillies powder, ginger and hing.

Remove the batter to a bowl and beat it well for 1/2 to 1 min to aerate the batter. Add cashews if using. Pour oil to a kadai and heat it enough to fry the vadas. Take small portions of the batter and drop into the oil and fry until golden and crisp. Remove to a plate.

Drop fried vadas to a bowl of water while they are still hot. Rest them for 20 mins. Timing may vary depending on the size of the vadas. Gently press down the vadas in between spatulas or your palms one after the other to remove excess water. Place them in a serving tray.

Beat yogurt until smooth and creamy. You can also add a tbsp of powdered sugar and little salt to the dahi.
Pour dahi over bhallas generously. Allow to rest for at least 15 mins.

Top dahi bhallas with a generous amounts of green chutney and sweet tamarind chutney.
Sprinkle cumin powder, chaat masala, black salt and red chilli powder. Garnish with coriander leaves. Adjust more or less dahi, chutneys, chaat masala, cumin powder and red chilli powder to suit your taste.
Serve dahi vada immediately after you sprinkle the spice powders.