Put the first five ingredients into a large 34cm x 26cm high-sided roasting tin with 100ml of the oil, 75ml of the Shaoxing rice wine and 2 tablespoons of soy sauce. Cover tightly with foil and cook for 35 minutes, until the shallots are soft but still hold their shape.
Stir in the grapes, cover again with foil and cook for another 10 minutes. Remove the roasting tin from the oven, take off the foil and set the tin aside while you prepare the sprouts. Increase the temperature to 220°C fan.
Mix the sprouts with the remaining 2 tablespoons of oil and ¼ teaspoon of salt, then spread out on two parchment-lined baking trays. Roast for 16 minutes, switching the trays halfway through, until the sprouts are browned.
Add the sprouts to the tin of grapes and chestnuts, gently mix everything together and leave, uncovered, at room temperature for 1 hour, if you can, or at least 30 minutes, for the flavours to develop.
Meanwhile, in a small bowl mix the chillies with the rice vinegar, sugar and ⅛ teaspoon of salt and leave to pickle for at least 30 minutes.
Once the Brussels sprouts have sat for a while, stir in the remaining tablespoon of Shaoxing rice wine and the remaining 2 tablespoons of soy sauce. Stir through the parsley and transfer to a large, shallow serving bowl. Top with the pickled chillies and the pickling liquid and serve.