Grilled mackerel and barbecued spanish onions with sweet and sour sauce

Method

Use either 4 grey (spanish) mackerel cutlets, about 2cm thick, or 4 whole and gutted blue mackerel. If these are unavailable, any oily fish such as large sardines, kingfish cutlets or whole small trevally are perfect for barbecuing.

For the sauce 

Make the sauce first by putting 1/2 a cup of sugar in a high-sided pot with 2 tbsp of water. Bring to the boil and keep it bubbling away until the sugar has caramelised to a light mahogany colour. Carefully pour in 750ml of red wine vinegar and keep it simmering until it reduces by half. Turn it off, transfer to a bowl and cool - it should be syrupy.

Cut 4 unpeeled spanish onions in half, brush with olive oil, sprinkle generously with smoked paprika and crushed fennel seeds, season with plenty of salt and pepper and grill on the barbecue. Brush the fish with olive oil, sprinkle with salt and place it on the barbecue. Brush some of the sweet-and-sour sauce on the top side of the fish before turning, then do the same to the other side.

When the onions have softened, remove their outer skins, place on a serving plate and sprinkle with a little sweet-and-sour sauce.

To serve 

Serve the fish with the onions and wedges of lemon.