Makes 20-24, depending on the size of your onions.
2 large (or 3 medium) yellow or red onions, peeled, sliced cross-wise into 1/4-inch rings (do not separate, but if the rings fall apart, do not fret)
2 cups besan (chickpea flour)
1/2 tsp cayenne pepper, or more or less to taste
1 tsp turmeric
1/4 tsp ground oregano, fennel pollen or cumin
1/4 tsp kosher salt
Oil for deep frying (peanut, canola or rice bran oil)
Raita, chutney or spicy tomato ketchup, for serving
Set the oil to heat in a deep fryer or deep sauce pan. In a large bowl, combine besan, cayenne, turmeric, oregano/fennel/cumin, and kosher salt. Stir with a whisk. Add enough water to make a batter the consistency of thick cream, so add the water slowly. Test the oil by frying a small bit of batter; it should sizzle immediately and rise to the top if the oil is hot enough.
Very carefully add 2-3 Tbsp of the very hot oil into the batter, and whisk to combine. The batter will sizzle, but this is what helps the bhajis crisp. In small batches, just a few at a time, dunk the onion slices into the batter and carefully drop into the oil. Don't crowd the pot, or the bhajis won't brown. Fry until golden all over, 2-3 minutes, turning occasionally. Lift onions out of the pot with a spider or strainer, and place on a platter covered with paper towels. Sprinkle with crunchy sea salt and serve hot, with raita, chutney or ketchup for dipping.