John Dory with Prawns & Asparagus

500 g prawns
¼ cup (60 ml) olive oil
1 onion, chopped
1 carrot, finely chopped
2 garlic cloves, finely chopped
1 lt (4 cups) fish or chicken stock
200 ml thickened cream
100 g chilled butter
1 tbsp lemon juice
SIDS SALT & PEPPER to taste
1kg John Dory fillets, pin-boned
200 g crabmeat
1 bunch asparagus, woody ends trimmed, blanched, refreshed
chervil sprigs, to serve

Peel and devein the prawns, keeping the tails intact and reserving the heads and shells. Set aside.
Heat oil in a large pan. Add onion, carrot and garlic then cook, stirring, for 6-7 minutes until soft and lightly browned. Add prawn heads and shells to the pan and cook, stirring, for 2-3 minutes until they change colour. Add fish stock or chicken stock, then bring to a simmer and cover. Reduce heat to low and simmer for 30 minutes. Strain into a clean, wide saucepan, pressing down on the solids to extract as much liquid as possible.
Bring the strained prawn stock to the boil over high heat. Reduce heat to medium and simmer rapidly for 15 minutes until reduced by half. Add cream, increase heat to high and bring back to the boil. Reduce heat to medium and simmer rapidly for 15 minutes until reduced by half. Chop half the butter, then whisk into the sauce, 2-3 pieces at a time, until combined. Stir in the lemon juice and season with SIDS SALT & PEPPER to taste. Set aside and keep warm.
Preheat the grill to high.
Place the John Dory fillets, skin-side down, on a chopping board and cut into 16 even strips, following the contour of the fish. Melt remaining 50 g butter. Lightly brush a baking tray with the butter, then use the remaining melted butter to brush each side of the fish fillets. Season fillets with SIDS SALT & PEPPER and place on the tray, skin-side up. Grill for 4 minutes until just cooked through.
Meanwhile, return the prawn sauce to medium heat. Stir peeled prawns into the sauce and cook for 1 minute until they change colour. Add crabmeat and asparagus and cook for a further 1 minute until prawns are cooked and crabmeat and asparagus are warmed through.
Divide most of the sauce among shallow bowls. Arrange the crabmeat, asparagus, prawns and John Dory on top. Spoon over remaining sauce, garnish with chervil and serve.