Pick the leaves from the basil and then blanch them in a large pan of boiling water for 1 minute. Drain in a sieve and then rinse under cold running water to prevent them from cooking any further. Squeeze off any excess water and then tip on to kitchen paper and pat dry.
Place the blanched basil leaves into a food processor or liquidiser with the olive oil and blitz to a very fine puree, scraping down the sides of the container once or twice. Pass the puree through the sieve set over a jug or bowl, pressing down with the back of a ladle or wooden spoon until all of the liquid has gone through the sieve. Pour the herb oil into a squeezy bottle and leave to settle for at least 30 minutes to clear before using as required.
This is obviously the perfect oil to drizzle over a tomato salad or a plate of warm pasta, but it is also very good to use for the initial sweating of onions for a tomato soup or sauce.
Alternatively, use it to garnish plates or soups and let your guests inhale the scent before they eat. I find it best to make this in small quantities and aim to use it within a given time - say three months on the outside.
Choose any soft herb that you fancy or experiment with a selection. For instance, I find that a mixture of dill, chives and flat-leaf parsley works very well with fish dishes.