Peel the parsnips and potatoes, then cut them into small chunks.
Peel, then finely chop the onion and ginger.
Heat the oil in a saucepan. Add the onion and sauté for 5 minutes, then add the garlic, ginger, and the coriander seeds. Cook for a minute, while stirring.
Add thee parsnip and potato pieces. Sauté for another 5 minutes, then add the stock. Bring to the boil, then simmer for 20-25 minutes over lower heat, until the vegetables are soft.
Using a stick blender, blitz until smooth and silky. Add more hot stock if you find it too thick.
Stir in the miso and soy sauce, then the lemon juice or vinegar.