Aubergine soup with cumin and minted yoghurt

I've been guilty of discovering a shrivelled aubergine in the bottom of the fridge. A good way to rescue it is to make this North African soup. My favourite spice, cumin, comes into its own here, adding a nutty, savoury tint to the blended aubergine. You can serve this chilled, at room temperature or hot, depending on how you're feeling. I prefer it at room temperature as the flavours come through most clearly then.

1 onion, peeled and roughly chopped
2 cloves of garlic, peeled and crushed
2tsp ground cumin
2tbsp olive oil
4 medium-sized aubergines, peeled and chopped
11/2 litres vegetable stock
Salt and freshly ground black pepper to serve
4tbsp thick greek yoghurt
1tbsp chopped mint leaves
1tsp cumin seeds, lightly toasted

Gently cook the onion, garlic and cumin in the olive oil in a thick-bottomed pan for 3-4 minutes until soft, stirring every so often. Add the aubergines and vegetable stock and bring to the boil, then season and simmer gently for 20 minutes. Remove from the heat and blend until smooth in a liquidiser and re-season if necessary. Meanwhile mix the yoghurt with the mint. Serve the soup with the yoghurt spooned into it or served on the side, and with the toasted cumin seeds scattered on top. Eat with flat bread or pitta.