Peel and finely chop the onion. Scrub and finely chop the potatoes. Scrub and peel the beetroot. Slice off a small wedge and set aside. Finely chop the rest of the beetroot (you may want to wear gloves).
Heat 2 tsp oil in a pan over a low heat. Add the onion, potatoes and chopped beetroot. Season well. Cover and cook for 8-10 mins till the veg are soft. Stir every so often. While the veg cook, shred half the cabbage as finely as you can.
Measure out 2 tsp of the cumin seeds and add them to a dry frying pan. Toast for 2-3 mins, shaking the pan, till they smell nutty and start to jump.
Add half the toasted cumin seeds to the veg pan along with the cabbage. Measure out 2 tsp of the honey and add to the pan. Crumble in the stock cube. Pour in 800ml boiling water and stir to dissolve the stock cube. Cover and bring to the boil.
Turn the heat down a little and simmer for 30 mins till all the veg are very soft. While the soup simmers, dice the reserved wedge of beetroot.
Remove the pan from the heat. Blitz the soup with a hand-held blender in the pan till smooth (you can leave it chunky if you prefer). Return to the heat for 1-2 mins to warm through. If it’s too thick, add more water. Taste and adjust the seasoning if it needs it.
Finely chop the chives. Ladle the soup into warm bowls. Top with spoonfuls of the yogurt, the diced beetroot and the rest of the toasted cumin seeds. Garnish with a few chopped chives to serve.