I use a vegetable peeler to peel away the strings from the celery, then cut it into chunks.
1 stick celery (and see above)
1 tsp capers, rinsed
1 tbsp wholegrain mustard
2 cloves garlic, roughly chopped
60ml olive oil
60ml rapeseed or sunflower oil
1 egg yolk
Put everything, bar the egg yolk, in the blender. Whizz until a slightly creamy, smooth-looking sauce is formed, then add the egg yolk and blend again. Season with salt and pepper to taste, pour into a bowl and chill until needed. Stir before serving, as the oil will separate slightly on keeping.
UPDATE: Just the other night I made a simple béchamel sauce for a pasta bake with salami and courgettes and, finding I hadn't made quite enough sauce, whisked in the remaining green sauce to increase the volume a little. Result? Totally divine In fact, this may now be one of the bet uses for my little green goddess! x