In a wide mouthed large bowl or pan, put 6-8 cups of yogurt. Add salt to taste.
Seasoning: In a pan put 2-3 tablespoons of oil and when hot add red chli, mustard seeds. When the seeds splutter, add chana dal, then urad dal. When they are golden brown, add jeera and curry leaves.
Add this to the dahi.
In a large wide mouthed bowl/pan, put half cup of buttermilk ( you can beat and dilute dahi and use) and add salt just ¼ teaspoon.
Put water for boiling on the side.
If you got frozen medhuwada, thaw them few hours before as many pieces as you want to make and keep them ready. (You can shift them from freezer to frigerator overnight).
Microwave them high for 1-2 minutes. Idea is to get them very hot not dessicate them. Put the boiling water in the buttermilk mix, and dunk these vadas for few minutes turning them on both sides.
They usually swell in volume. After few minutes transfer them without breaking on to the Dish with the seasoned dahi. Let them soak some more before transferring to serving bowl.
Garnishing:
Garnish with thin sev, boondi, date/tamarind, or green coriander chutney and pomegranate seeds and cilantro.
Garnish just before serving.