Drain the kimchi in a sieve over a measuring jug (you'll need about 100ml brine, so top up with more from the jar if needed). Heat the oil in a large saucepan over a high heat and fry the drained kimchi, brown onion and pork belly for 5 mins. Stir in the gochugaru and sugar, then fry for another 2 mins. Pour in 800ml water and the reserved kimchi brine, then bring to the boil. Simmer, uncovered, over a high heat for 15 mins.

Slice the tofu into 5cm squares that are about 1cm thick, then arrange these over the kimchi jjigae. Cover the pan with a lid and cook for 3-4 mins, or until the tofu is heated through. Scatter over the spring onions to serve.