1. Preheat your oven to 220°C/Fan 200°C/Gas 7. Fill your kettle and boil it. Trim and peel the butternut squash. Halve it and scoop out the seeds. Chop the squash into 1-2cm-thick pieces and scatter into a roasting tin. Toss the squash with 1 tsp oil and a pinch of salt and pepper. Slide into the oven and roast for 30 mins, till tender and caramelised.
2. Meanwhile, pop the dried porcini mushrooms into a small heatproof bowl and cover with boiling water. Leave for 15 mins to soak. Once soaked, drain the mushrooms and rinse well under a cold tap. Shake any excess liquid from the porcini and set them aside.
3. Peel and finely chop the onion. Peel and finely chop the garlic cloves (set 1 chopped clove aside for later). Strip and finely chop the rosemary leaves. Trim any ragged leaves off the Brussels sprouts, and cut the sprouts into quarters. Roughly chop the kale, discarding any thick bits of core.
4. Pour 800ml boiling water into a pan and bring to the boil. When the water is boiling, slowly trickle in the polenta, stirring as you add it, to keep the mixture smooth. Once all the polenta is added, turn the heat down very low, pop on a lid (or use a baking tray if you don’t have a lid) and cook, stirring often, for 10 mins till the polenta has thickened a little.
5. When the squash has roasted, tip it into a bowl and roughly crush with a fork or masher. Add 1 chopped garlic clove and grate in the lemon zest. When the polenta is cooked, fold through the mashed squash. Add a little salt and pepper. Take off the heat but cover again to keep warm.
6. Pour 1 tsp olive oil into a large frying pan and warm to a medium heat. Slide in the onion, remaining garlic and rosemary. Add a pinch of salt and pepper. Fry for 3-4 mins to soften slightly. Add the sprouts, porcini and kale. Continue to fry for 5 mins, stirring occasionally, till tender.
7. Pour 4 tbsp soya cream into the frying pan and stir it through the veg. Warm through for 1-2 mins.
8. Divide the butternut polenta between a couple of warm plates or bowls, top with the creamy mushrooms and veg and serve straight away.