Step 1
Preheat oven to 160C fan-forced (180C conventional). Line a tray with baking paper and, on it, place the sliced onion and sliced garlic. Toss with a tablespoon of olive oil and a pinch of salt and set aside.
Step 2
Season both sides of your fish fillets with salt and pepper and set aside.
Step 3
Lay one fish fillet, skin side down, on your chopping board. Under it place three long pieces of butchers string, which you’ll use to tie both fillets together. Mix all the filling ingredients together and pile on top of the first fillet. Place the second fillet on top of the filling, in the same orientation as the bottom piece, and use the string to tie the two pieces together like a sandwich. Not too tightly, though: you just want to hold the pieces together. Gently transfer the fish to the tray with the onions.
Step 4
Splash the top of the fish with the wine and lime juice and season with a little salt and pepper. Place a bay leaf under two of the tied strings and dot the top of the fish with the soft butter. Place the tray in the oven to bake.
Step 5
Bake the fish for about 40 minutes until cooked through. Remove from the oven and allow to rest with a piece of foil gently tenting it for about 10 minutes.
Step 6
While the fish is resting, make the tartare sauce by mixing together all the ingredients in a bowl.
Step 7
Finally, cut the strings from the fish and discard. Cut the roasted fish into slices and serve with the tartare sauce.
