If onion squash is hard to find, you can substitute butternut squash; the skin will need to be removed, but otherwise treat it in exactly the same way.
1 onion squash, sliced in half, deseeded, skin left on
1 dried chilli, crumbled
4 tbsp olive oil
Sea salt and freshly ground black pepper
1 red onion, outer skin removed and sliced into 1/8-inch rounds
2 tbsp balsamic vinegar
1 bunch of sprouting broccoli, washed, patted dry and sliced into six long slices, including the stems and outer leaves
For the dressing
100g/31/2oz whole hazelnuts
1 tbsp Dijon mustard
1 tbsp red-wine vinegar
120ml/4fl oz extra-virgin olive oil
First make the dressing: preheat the oven to 180C/350F/Gas4, lay the hazelnuts on a tray and place on the middle shelf of the oven for five minutes to tickle out their flavour and colour them slightly. Place the anchovies and mustard into a mortar and pound with a pestle until you have a rough paste. Add the hazelnuts and vinegar and pound once more. Pour in the oil and stir well to combine. Taste and season with a little salt and pepper if needed.
Now turn up the oven to 200C/400F/ Gas6. Lay the slices of squash on a baking tray, crumble over the chilli, pour over two tablespoons of the oil and season with the salt and pepper. Cover with foil. Bake in the oven for 40 minutes, uncovering for the final 10; the squash should be tender but not falling apart. Remove from the oven and set aside.
While the squash is cooking, place the onion rounds in a smaller baking tray and add the balsamic and remaining olive oil.
Season with a little salt and pepper, cover with foil and roast in the oven for 20 minutes, then, as with the squash, uncover and cook for a further 10 minutes; the onions should look glossy and turn a deep purple in colour.
Place a large pot of well-salted water on to boil, prepare the broccoli and, when the water is boiling, plunge the broccoli in and cook for two to three minutes; drain but do not refresh.
Arrange the warm vegetables on a plate, spoon over the dressing and serve, adding some roasted cherry tomatoes if you wish.