Preheat the oven to 180°C fan/200°C/ gas 6. Carefully halve the squash, remove the seeds, then place cut side down on a board. Cut almost all the way through the squash, but not quite – you want a series of parallel cuts, as if making a hedgehog.

Stuff each cut alternately with rosemary, thyme and bay, then transfer to a roasting tin along with the onions and leeks. Lay the sliced butter over the squash and onions, and season with the sea salt. Pour the stock into the tin, then transfer to the oven and roast for 1 hour 10 minutes.

Prod the softened leeks with a wooden spoon and stir through the crème fraîche. Scatter the crumbled feta over the squash, and serve alongside the onion and leek gravy.