Do not overcrowd the pan or kadai. Overcrowding the pan will lower the oil temperature and as a result the vadas will soak more oil. The vada also expand a bit while frying.

Chana Dal (split gram lentils): Using only maash ki dal can give one-dimensional flavor, so many recipes add moong dal along with maash. Chana dal, though not so commonly used, gives a beautiful flavor and texture to the bhallas. You could try using equal weight in moong dal but I’ve yet to try it myself. Pour the whisked yogurt over the vadas. Let the vadas rest for at least 30 minutes in yogurt to absorb the flavors. Refrigerate if planning to serve it later. Soaking lentils: To get a good soft urad dal vada, remember to soak the lentils for 4 to 5 hours or overnight. Grind the batter really well. Dahi Vada are a popular street food from North India. “Dahi” means yogurt and “Vada” means deep fried fritters or dumplings, and the recipe is about as straightforward as it sounds.Immerse in beaten yogurt for 10 mins. Garnish with roasted cumin seeds, red chili powder, salt, coriander leaves, tamarind sauce, and yogurt. Serve cold. Dahi Bhallas are festive and people often make them during holidays like Ramadan and Eid. Dahi Bhalla vs Dahi Vada

What are the main ingredients used here? Any added preservatives, additives or flavor enhancers used?

Gits Dahi Vada 

Delectable! These dahi vadas taste brilliant as is or can be served alongside any dip of your choice. Well salted dahi vadas that do not require any further adjustments. No garlic version: To make a no-garlic version dahi vada, just skip adding the garlic in the green coriander chutney. Aromatics: Fresh ginger root adds a nice zing to this batter, and Serrano chili adds a subtle peppery taste. Remove the ribs and seeds for a milder flavor. For Yogurt Sauce (Dahi): Wrap the dish in plastic cling wrap or transfer to a container with a lid, and keep leftover dahi vada in the refrigerator overnight or for a day only. Any longer and the taste of the yogurt changes. from what i have seen and eaten, the thayir vadais have always been donut shaped. even here in the south indian restaurants the thayir vadais are like medu vada.