First of all put urad dal in water and soak it for 6 hours at least, now drain the water and put dal in a mixture blender and blend it to make smooth paste.
Give it rest for 3 hours, after 3 hours add in salt and mix it well in one direction so it will be fluffy.
Now heat oil in a deep pan, make small vadas from urad dal paste and fry in hot oil till become light golden brown.
Now take warm water in a big bowl add in salt and mix well, now add in fried vada and keep them in water for 5 minutes.
After 5 minutes press the vadas with hands so excess water drains out and put vadas in a plate.
Now put vadas in a serving bowl, now first put curd on them then jaggery and tamarind chutney, green chutney, roasted cumin and fennel seeds and finally sprinkle little red chilli powder and chaat masala.
Now the delicious dahi vada is ready to serve.