Green sauce (whether it's pesto, chimichurri, salsa verde, or the like) and yogurt sauces are both familiar friends of ours.
But while the two often mingle—see, in Ottolenghi's Plenty More, the Mixed Vegetables and Yogurt with Green Chile Oil (cooked tomatoes, zucchini, eggplant, and peppers are tossed with yogurt mixed with garlic, fresh and dried mint, and lemon juice and drizzled with a super-spicy blend of green chile, oil, parsley, and mint)—they don't normally mix entirely.
Yogurt sauces are often flecked with herbs (in tzatziki, for example), or used as landing pads, soothing dollops, or rich accompaniments for spicy, green sauce-basted meats and vegetables. A full fusion of the two parties, however, seems less common—but makes a whole lot of sense!
Instead of adding herbs to yogurt, I've started going in the other direction: adding yogurt to herb-heavy green sauces—a subtle distinction that's made my green sauces more versatile. Because while we often hail blends of herbs and alliums and salty players like anchovies and preserved lemons for being brighteners and sharpeners—they're "heady", they're "piquant"—I find they can be too much so. And the best way to round them out is to add yogurt (which, it just so happens, I'm often trying to use up).
So to my garlic scape pesto, I add a tablespoon of Greek yogurt (or plain yogurt or goat's milk yogurt) to calm it down: It thickens it, neutralizes it, and emulsifies it—transforming it into more of a dip or a smear than a pasta-tossing sauce or a thin marinade. Adding yogurt accomplishes the same effect as adding a hard-boiled egg (as is the case in the genius Silver Palate Green Sauce) or even a soft-boiled one (in Eric Korsh's Dill Vinaigrette). Or, think of it as a much thicker, much quicker Green Goddess.
I like to keep an unadulterated green sauce in a jar in the fridge, aiming to use them up within five days or so. It can serve as a marinade or a dressing, yes—but, blended with as much yogurt as I like, it can turn, quickly, into a baby pool for my vegetables or a thick spread on bread.
How do you make your green sauce work for you? Share ideas in the comments below!