Trim the roots from the brussels sprouts and remove the dark outer leaves
Fry the leaves at 170°C in clean oil until crisp, then place on absorbent paper and season with salt. Keep warm in a low oven until you’re ready to serve
Place onions in a heavy based casserole and slowly brown in a little butter. Cook until the onions just begin to soften, then add the chestnuts and remaining butter. Brown, then add the brussels sprout hearts and all remaining ingredients
Season to taste and cover with a disk of baking paper. Place into the oven at 170°C and cook until the chestnuts are just tender (pay attention, as they will break up if overcooked)
Remove from the oven and check seasoning
TO SERVE
Serve the brussels sprouts in a deep serving dish, using the crisp outer leaves as a garnish