Tuna Carpaccio

Step 1: Combine the sliced onion and vinegar in a small bowl. Set aside for 15 minutes to soften. You will have more than needed; use as much as you like.

Step 2: Mix the lemon juice, olive oil and sugar in a small bowl. Set aside.

Step 3: Place one piece of tuna on its flat side between two sheets of go-between or baking paper on a chopping board. Using a rolling pin, gently tap and roll it until about 2 mm / 0.08 in thin. Do not smash it.

Tip: Turning the tuna onto its flat side before flattening works across the muscle fibers and helps give it a fine, delicate texture.

Step 4: Place the tuna flat side down in the middle of a plate, then slowly peel off the plastic sheet or paper.

Step 5: Flatten the second piece the same way and return it to the chopping board. Cut it into pieces to fill the empty spaces, then arrange them over the plate to make a thin, even layer of tuna.

Step 6: Gently brush the lemon vinaigrette over the tuna.

Tip: Dress the tuna just before serving; the lemon can begin to change the fish if it sits for around 15 minutes.

Step 7: Sprinkle with salt flakes, Espelette pepper and chives. Top with a few slices of pickled onion and edible flowers, if using.

Step 8: Serve immediately with crostini on the side.

Step 9: Preheat the oven to 180°C / 350°F (160°C fan-forced). Brush both sides of the bread with oil and sprinkle with a little salt. Arrange in a single layer on a tray. Bake for 15 minutes, turning halfway, until crisp. Cool on the tray before using.