Peel and thinly slice 250 grams of onions. In a mixing bowl, combine the sliced onions with 1 teaspoon of salt and set aside for 10 minutes to release the moisture.
In another bowl, mix 100 grams of besan (gram flour), 1 teaspoon of red chili powder, 1/2 teaspoon of turmeric powder, 1/2 teaspoon of garam masala, 1/2 teaspoon of ajwain (carom seeds), and a pinch of baking soda. Gradually add water to form a thick batter.
Squeeze the excess moisture from the onions and add them to the batter. Mix well to ensure the onions are evenly coated.
Heat oil in a deep frying pan over medium heat. Once the oil is hot, carefully drop spoonfuls of the onion batter into the oil. Fry the bhajis in batches, turning occasionally, until they are golden brown and crispy.
Remove the onion bhajis from the oil using a slotted spoon and place them on a paper towel to drain excess oil. Serve hot with mint chutney or ketchup.