Squash and smashed sausage gratin, with grain mustard and sage

Pumpkins and squashes herald the start of autumn, when thoughts turn to cooking warming, nourishing food. This is when these versatile ingredients shine. Varieties are countless, but worth a special mention are crown prince, butternut and - my favourite - delica, with its dense, intensely sweet, rich and buttery flesh. Always look for bright skin without blemishes and ensure it is firm to the touch. Gratins are the ultimate one-pot wonder. A good one delivers bags of pleasure and this dish is no exception. Here, the flavour that comes from the squash ties in brilliantly with the mustard and the sage.