1. About 30 minutes beforehand, remove
the fish from the fridge
and let it come to room temperature.
2. For the agrodolce onions, heat the olive oil in a saucepan over
medium-low heat. Add the onions and cook gently for 5 minutes,
then add the remaining ingredients with 1⁄4 cup (60ml) of water and
stir well. Turn the heat up to medium and cook until reduced by
quarters, with a beautiful sweet-sour flavour. Remove
from the heat and leave to cool to room temperature.
3. Heat the barbecue to hot and clean the grill bars. Brush the tuna
with olive oil and sprinkle liberally with salt. Put it on the grill at a
45-degree angle to the grill bars and cook for 2 minutes, then rotate
to 45 degrees in the opposite direction and cook, still on the same
side, for a further 2 minutes – this will give the fish nice criss-cross grill
marks. Now turn the tuna over and cook for a final 3 minutes.
4. Place the tuna on a chopping board and cut each steak in half at an
angle to expose its beautiful, rare centre. Place the fish on four plates
and spoon the agrodolce onions over the top. Give it a good grind of
pepper and a drizzle of olive oil, then serve.