4 tbsp ready-made chilli and garlic sauce
3 garlic cloves, peeled and crushed
2cm/1in fresh root ginger, peeled and finely chopped
2 bunches mixed herbs (such as chervil, parsley, dill, mint, tarragon and basil)
2 tbsp balsamic vinegar
1 tsp caster sugar
150ml/5fl oz olive oil
90ml/3fl oz olive oil
12 large prawns, head and tail left on, body peeled, de-veined