Peel and finely grate the ginger and garlic. Roughly chop the tomatoes. Halve the chilli and flick out the seeds for less heat. Finely chop it. Peel and chop the sweet potatoes into 2cm cubes.
Place a deep pan on the hob for a couple of mins. When warm, add in 1 tbsp oil. Add the ginger, garlic, coriander seeds and star anise. Fry for a min. Add the tomatoes and chilli. Fry for 5 mins stirring regularly till the tomatoes are soft.
Crumble the stock cube into a jug. Pour in 400ml boiling water. Squeeze in the green Thai paste and peanut butter. Swirl together.
Drain and rinse the chickpeas.
Add the sweet potatoes and drained chickpeas to the pan. Stir to coat in the tomatoey sauce. Pour in fragrant stock. Pop a lid on the pan for 12 mins.
Finely shred the spring greens. Finely chop the coriander stalks, keeping them separate from the leaves.
The sweet potatoes should just be cooked. If they are still hard, cook for a few mins more. Taste and adjust the seasoning. Add the shredded spring greens and coriander stalks and stir. Pop the lid back on for 3 mins.
Spoon the curry into warm shallow bowls. Scatter over the coriander leaves.