1.Place stock, star anise, cinnamon stick, ginger, soy sauce and brown sugar in a medium saucepan over high heat. Cover; bring to the boil. Reduce heat and simmer, covered, for 5 minutes.
2.Meanwhile, soak noodles in boiling water in a large heatproof bowl for 10 minutes: stir noodles to separate strands, then drain.
3.Add tofu to stock: simmer for 5 minutes. Divide noodles among serving bowls. Ladle hot stock and tofu over noodles (discard spices). Top with herbs, sprouts, chilli and onion. Serve with lime or lemon wedges.
Pho is Vietnamese soup. Use Vietnamese mint and Thai basil if available. Make ahead Cook stock mixture the day before; keep, covered, in the fridge.