Toast the walnuts in a dry pan for just a couple of minutes until they release that gorgeous nutty aroma. Don't get side-tracked when you do this as these little beauties can catch very quickly and go from toasty tastiness to burnt offerings within seconds!
Core the apple but don't peel it as the little flecks of red skin look pretty and the skin is full of vitamins too.
Chop the celery and toss this into a food processor along with the apple and the coriander leaves.
Season with salt and pepper and whizz that processor till you get a lovely bright green paste.
Drizzle in the olive oil a little at a time until you get the consistancy you prefer. If I were mixing this with pasta I would add more oil for a looser sauce, when serving with a sandwich I add less oil for a firmer sauce that won't drip everywhere.
Spoon your pesto into a small jar with a lid and top with a little more oil to seal and stop the herbs oxidising and darkening in colour. Store in the fridge for up to a week.