Chop and discard the root ends off the Brussels sprouts and thinly slice the heads into shredded leaves. Thinly slice the onion and set veggies aside.
In a large bowl, whisk all the dry ingredients together. Add the veggies and toss them into the dry mix with your hands, coating everything as evenly as possible. Add the ¼ cup water 1 Tbsp at a time. After adding ¼ cup, let the mixture sit for at least 3 minutes. There should still be some dry spots in the mix. In this time set a small cast iron or heavy pot with at least 3 inches of neutral oil (canola or vegetable) on medium high heat, reaching at least 350 degrees F. Place a paper towel lined wire rack next to the frying station.
With a spoon, mix the pakora mixture again, adding 1 Tbsp of water at a time, until the veggies look evenly coated and can loosely adhere in a clump when spooned together. Add a small piece of pakora batter into the oil to test the heat. If it bubbles and rises to the top immediately, the oil is ready.
Using a tablespoon, spoon clusters of pakora batter into the oil, taking care not to overcrowd the frying vessel (or else they’ll get soggy)! Fry the pakoras for 2-3 min per side, or until deeply golden brown all over. Using a spider, transfer pakoras to the lined wire rack and let cool. Eat and serve immediately with chai and chutney!