Tuna à la Bordelaise

Pat the tuna steaks dry with kitchen paper, then season all over with half the salt and all the pepper. Finely slice the onions, shallots, and garlic. Crush the tomatoes by hand in a bowl. Mix the chopped parsley, capers, and lemon zest together as the gremolata garnish.

Heat the olive oil in a wide, heavy-based casserole over high heat until shimmering. Sear the tuna steaks for 90 seconds per side until deeply golden, then transfer to a plate — they will finish cooking in the braise.

Reduce the heat to medium-low and add the butter to the same pan. Add the onions and shallots with the remaining salt and cook, stirring occasionally, for 18–20 minutes until deeply softened and beginning to turn golden at the edges.

Add the garlic and cook for 2 minutes until fragrant, then stir in the tomato purée and cook for a further 2 minutes until it darkens slightly and coats the vegetables.

Scatter the flour over the vegetables and stir continuously for 1 minute to cook out the raw flour taste.

Pour in the white wine, stirring to lift any fond from the base, and let it bubble for 3 minutes until the sharp alcohol smell mellows.

Add the crushed tomatoes, fish stock, bouquet garni, and sugar. Stir to combine, then simmer uncovered for 10 minutes until the sauce reduces slightly and coats the back of a spoon.

Nestle the seared tuna steaks into the sauce, spooning the sauce over them. Reduce the heat to the lowest setting, cover with a tight-fitting lid, and braise for 12–15 minutes until the tuna reaches an internal temperature of 63°C when checked with a meat thermometer — the flesh should be just opaque through to the centre.

Remove the bouquet garni. Taste the sauce and adjust seasoning. Scatter generously with the parsley, caper, and lemon zest gremolata and serve directly from the casserole with lemon wedges alongside.