Roughly chop your carrots, potato, onion and celery, big chunks are fine. Crush the coriander seeds using a mortar and pestle. If you don't have a set, no prob, just put the seeds in a sandwich bag and crush with something heavy e.g. a rolling pin.
Put a big pot on a medium-high heat. When the pot is hot dry fry your crushed coriander seed. When you're getting a lovely smell and the coriander has browned a little pop it onto a plate to one side. Put the pot back on the heat and glug in a tablespoon of olive oil. Throw in a piece of onion, if it sizzles the pot is hot! Chuck in all your veg, stir around a bit to coat in oil and pop the coriander back in.
Now reduce the heat a little, stick on the lid on the pot and leave it there to sweat like a naughty kid outside the principles office. After 10 minutes give it a stir and a check. Let them stew away for about 20 minutes. When the veggies are soft (you can easily slide a knife through them) add your veggie stock and boiling water.
Take the soup off the heat and blend with a hand blender. Add a tin of coconut milk and put back on the stove if this has reduced the temperature (I don't like my soup to hot, so I am usually happy with it as is!).