fresh basil leaves, to garnish
1 garlic clove, chopped
½ lemon, juice only
1 sprig fresh rosemary, chopped
100g/3½oz Kalamata olives, pits removed
salt and freshly ground black pepper
1 tbsp olive oil
2 tbsp olive oil
25g/1oz butter
1 mackerel fillet, cut in half, skin scored with a sharp knife