Soak the shiitake mushrooms for 15 minutes in 100ml (3½oz) boiled water.
Put the shiitake and the soaking liquid into a slow cooker with the ginger and kombu and 700ml (1½pt) hot water.
Cover and cook on low for 3 hours, or high for 2 hours.
Remove and discard the ginger and kombu.
Meanwhile, continue with the tofu.
Stir any marinade left into the slow cooker pot with the garlic, chilli sauce, edamame, and broccoli.
Cover, turn the temperature to high, and cook for 15-20 minutes until the broccoli is just tender.
Cook the soba noodles according to the packet instructions.
Drain and divide between 4 bowls and scatter over the spring onions.
Ladle the broth over the noodles and top with crispy tofu and sesame seeds.