Heat a large chargrill or barbecue on medium–high heat. Add the onions and grill until charred, about 5 minutes. Set one onion aside for later use. Combine the chicken stock with the remaining charred onions in a bowl and steam over a double boiler for 4 hours. Pass the mixture through a fine sieve and put it in a clean saucepan over medium heat. Reduce the liquid by two-thirds.
Meanwhile, put the bonito fillets in a non-reactive container. Sprinkle with the salt and sugar and stand for 3 hours in the refrigerator. Wipe the fillets clean.
Cold smoke the fillets by preheating a coal-bedded kettle barbecue to low heat and set it up for indirect grilling using the top rack. Add half of the wood chips around the coals and cook for 3–4 minutes until smoke appears. Place the fillets on the oiled top rack, cover with lid and smoke at medium–high smoke, being careful not to cook the fish at all. You can add a tray of ice to help keep it cool. Alternatively set a piece of wood over a fire, snuff it out and put it in a tray. Place the bonito in a perforated tray that fits snugly over the other tray and cover with foil.
To assemble, cut the mirabelle plums in half, remove the stone and lightly salt the flesh. Sear the plums, cut side down, in a frying pan over medium heat.
Separate layers of the reserved onion and drizzle with Banyuls wine vinegar. With the sharpest knife possible slice two pieces of fish per person. Place two slices of fish on each plate. Add two seared plum halves and pieces of reserved onion. Lightly dress with the onion sauce and serve.
© 2014 All rights reserved. Published by Murdoch Books.