Ottolenghi's roasted butternut squash with cardamom and nigella seeds

This recipe for roasted butternut squash with cardamom and nigella seeds by Ottolenghi was in last weekend's Guardian. I was particularly tempted by the combination of cardamom with the squash, and the dollops of yogurt on top made it sound so fresh despite the intense spices, which also include cumin, coriander, tumeric and cinnamon as well as a green chilli. I'd never even heard of nigella seeds before, so there was an element of novelty there. This dish gave off wonderful aromas from the start. First you fry red onion in butter and olive oil, to which you add the butternut squash cubes. That alone was heavenly. So you can imagine the rising anticipation once it was all roasting in the oven with the spices and stock. Absolutely divine. And very easy to make :) Vegan version: no yogurt. I served it with slow roasted tomatoes tossed together with cous cous.