Heat a pan one-third filled with vegetable oil for deep-frying, until a breadcrumb will sizzle gently in it. (CAUTION: Hot oil can be very dangerous. Do not leave unattended.)
Place the flour in a bowl with the baking powder and whisk in enough water to make a smooth batter, the consistency of double cream.
Dip the squid in the batter to coat.
Deep-fry in the hot oil for 3-4 minutes, or until crisp and golden. Remove from the oil with a slotted spoon and drain onto kitchen paper.
For the chutney, heat the onion, tomatoes, sugar, balsamic vinegar and coriander in a pan for 8-10 minutes, or until soften.
Transfer to a serving plate and serve the tempura squid alongside.
