Grate the Jazz apple and squeeze out most of the juice. Reserve the juice. Place the grated apple in a bowl with ice-cold water. Slice the onion and add to the bowl.
Add the gram flour and baking powder to a large mixing bowl, then add the chilli powder, turmeric, chopped chilli and a pinch of salt. Mix in about 100ml of apple juice (add more water if need-be) to make a thick batter.
Add a splash more if it feels too stiff, but remember it’ll begin to hydrate after a while as the apple and onion contain moisture.
Drain the onion and apple well and mix it into the batter. Heat about 5cm of oil in a deep pan or deep-fryer to 180°C.
Lower heaped tablespoons of the bhaji mixture into the pan, a few at a time, and cook for a few mins, turning once, until they are evenly browned and crisp.
Drain on kitchen paper, sprinkle with a little salt and keep warm while you cook the rest.