Bring a medium saucepan of water to the boil for the noodles. Discard the husk and silks from the corn. Slice the kernels from the cob, reserving the cob. Crush or finely chop the garlic. Finely grate the ginger. Pick the coriander leaves, then finely chop the stems.
Step 2 — Make broth
Crumble 3 stock cubes* into a separate medium saucepan. Add the corn kernels, corn cob, garlic, ginger, coriander stems, 1 tsp sugar, 1 tbs soy sauce and 875ml (3½ cups) boiling water. Bring to a simmer. Reduce the heat to medium, cover and cook for 10 mins to develop the flavour.
Step 3 — Finish prep
Meanwhile, halve the carrot lengthwise and thinly slice on an angle. Coarsely chop the pak choy, keeping the stems and leaves separate. Thinly slice the tofu. Thinly slice the chilli, removing the seeds if less heat is desired (the chilli isn't essential to the dish, so omit it if you don't tolerate heat).
Step 4 — Cook noodles
Cook the noodles in the pan of boiling water for 7 mins or until tender. Drain, then rinse under hot water to prevent the noodles from sticking.
Step 5 — Cook carrot
Add the carrot to the broth and cook for 2 mins. Remove the corn cob and discard.
Step 6 — Finish soup and serve
Add the pak choy stems to the broth and cook for 1 min. Add the pak choy leaves and cook for a further 1 min or until just wilted. Divide the noodles and tofu among bowls and ladle over the soup. Scatter with the coriander leaves and chilli, if desired, to serve.