Preheat the oven to 230˚C.
Leaving the cauliflower whole, remove the outer leaves and place it on an oven tray. Drizzle with olive oil and a hefty sprinkle of sea salt and bake for 45 minutes. The top will colour and give the cauliflower the most amazing nutty flavour. Once cooked, leave the cauliflower to cool, then break it down into small florets.
Meanwhile, to pickle the grapes, heat a large heavy-based frying pan over high heat until smoking hot. Throw in the grapes and shake them in the pan for about 10 seconds or until blistered and scorched. Add the vinegar and continue to shake the grapes around the pan for another 5 -10 seconds. Pour the grapes and the liquid into a bowl and cover them with olive oil.
To make the dressing, whisk together the red wine vinegar, honey, mustard, salt and pepper. Slowly drizzle in the vegetable oil and continue to whisk until emulsified.
To assemble the salad, combine the cauliflower florets, shallots, parsley, hazelnuts and pickled grapes in a large mixing bowl. Splash in a couple of tablespoons of the dressing and season to taste with salt and pepper. Gently mix the salad, then place in a serving bowl and give it a light dusting with sumac to finish.