Sure, any potato salad will turn green if you leave it out long enough. (Not recommended.) But this potato salad gets its vibrant green color and tangy bite from fresh sorrel.
Sorrel looks like spinach, tastes like sourgrass, and is in season right now. If you grew up around here, the taste will remind you of oxalis — the yellow-flowered, clover-leafed weed whose stems we all chewed on despite our mother’s warnings that dogs pee on it. (Both plants contain oxalic acid, so skip it if you’re prone to kidney stones.)
You can use sorrel raw or cooked, though when you cook it the color turns dull and the leaves melt down into an unpleasant-looking goo — sorry, but it’s true — so if you’re going for appearance, use it raw.
Because it’s so sour, sorrel does best in recipes with some creamy and/or starchy elements to balance it out. Both Yotam Ottolenghi and Deborah Madison blend sorrel with thick, creamy greek yogurt to make a dressing — he adds garlic, olive oil, and dijon mustard; she adds walnut oil, sour cream, parsley, watercress, chives… you know, just check out her recipe, it’s good.
I made my potato salad with a simplified approximation of Madison’s sorrel sauce. (I suspect hers is even better than mine, but I didn’t have any watercress and only a little bit of parsley. And also I didn’t really measure anything. So if you like reliable results, use her recipe. Still, mine was pretty tasty.) The sauce also works well as a dip for vegetables and such, if you’re making it for a party and have a little extra.
- Potatoes (look for "waxy" or "boiling" potatoes, not baking potatoes)
- 1 bunch of sorrel
- 1 big glug of walnut or olive oil
- 1 container of greek yogurt
- (optional: parsley, watercress, other peppery cress, chives...)
- 1 hard-boiled egg yolk (if you don't happen to have a hard-boiled egg yolk sitting around, just crack an egg, put the yolk into a pan, and scramble it)
- 1 or 2 cloves garlic
- Wash and scrub the potatoes. Put them in a pot of salted water, boil them until they're tender, and drain. If they're large, chop them into potato salad-sized pieces.
- Meanwhile, wash the sorrel, remove and discard the stems, and tear up the leaves. If you grew the sorrel in your garden, check for slugs, too.
- Put everything EXCEPT THE POTATOES into your food processor and whirl until smoothish. Taste the sauce and add more salt, pepper, or garlic.
- Note: The first time I made this, I whirred the greens, garlic, and oil first, to make sure they were shredded nice and fine. This required that I stop and scrape down the sides of the food processor every ten seconds. The next time I made this, I just dumped everything in at once and it was fine.
- Pour the sauce over the potatoes, and toss gently to coat the potatoes. You can serve it warm or cold; if you're making it in advance, keep it in the fridge until you're ready to eat it.