Sorrel.

Sour power: Yotam Ottolenghi's sorrel recipes | Life and style | The Guardian:
From plot to plate.
Rhubarb, celery and sorrel salad.

This crunchy, crisp, sharp salad is ideal for spring and early summer.
The addition of raw rhubarb is a wonderful way to add even more vigour to an already hyper-punchy combination.
Serves four.

50g red quinoa
40g radishes (about 3 small ones), cut into 3mm slices (I use a mandoline)
130g rhubarb (about 1½ stalks), cut diagonally into 3mm slices
100g celery (about 2 stalks), cut diagonally into 3mm slices
50g parmesan (or vegetarian alternative), finely shaved
1 granny smith apple, cored, quartered and cut into 3mm wedges
80g watercress

For the dressing
90g sorrel leaves
5 tbsp olive oil
½ tsp Dijon mustard
2 tsp white-wine vinegar
1½ tbsp soured cream
Salt

Bring a medium saucepan of water to a boil. Add the quinoa and gently simmer for about 12 minutes, until cooked but still al dente.
Strain, refresh and drain.

Put all the dressing ingredients bar one tablespoon of oil into the small bowl of a food processor, add three-quarters of a teaspoon of salt and blitz smooth.

Put all the salad ingredients in a large bowl.
Pour over the dressing, add the remaining tablespoon of oil, mix together gently and serve.
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