Baking soda falls into that category of ingredients that you rather know what they do, but have some trouble giving a concise definition of when asked. Baking soda is a bicarbonate of sodium that reacts with acid to form carbon dioxide. It helps dough rise, gives breads a fluffy consistency and imparts an airy crispness to fried foods – three qualities prized in the Desi cuisine of South Asia. Onion bhajia, of Desi cuisine, are crunchy, delightfully moreish, sliced-onion fritters common to India. Like curries, spices used in bhajia depends on the region -- and usually the family making them -- but the base ingredients are the same. Bhajia made with baking soda fries up crispier and airier than those made without.
Beat 2 whole eggs in a mixing bowl using a whisk and add 3/4 cup of all-purpose flour. The ratio of 2 eggs to 3/4 cup of flour forms the base of bhaji batter, and makes one batch of 10 to 12 bhajia. Traditional bhajia use chickpea flour, but all-purpose flour works fine.
Add 1/4 teaspoon of baking soda, 1/4 teaspoon of cornstarch and 1/2 teaspoon of cream of tartar to each batch of bhaji batter. Whisk until free of lumps and aerated.
Add 2 finely sliced, medium red onions to every batch of batter. Add spices to the batter to taste. Traditional onion bhajia contain combinations of minced garlic, turmeric, chili powder, minced chilis, freshly chopped coriander and cumin seeds.
Fry the onion bhajia in 1 inch of 350-degree-Fahrenheit oil in a cast-iron skillet until golden brown all over, about 1 to 1 1/2 minutes total. Use an oil with a high smoke point, such as peanut, sunflower or walnut. Remove the bhajia from the oil using a slotted spoon and place them on a plate lined with paper towels to drain.