Halloween may be over but the season for pumpkins and squash is not; these sweet-fleshed vegetables will be with us until the end of the autumn. There are many varieties, each with their own, subtle taste, and a glorious array of colours. The bright-orange onion squash – so called for its shape – is my favourite. Its flavour isn't particularly sweet, but it is deep and rich. It won't disintegrate during cooking, and works beautifully with roast lamb or chicken. Do leave the skin on – it's almost the best part.