Watercress Sauce

Watercress sauce is the kind of cold green sauce that makes a plain piece of fish look like restaurant food. Raw watercress gives it a peppery bite somewhere between arugula and horseradish, while yogurt and mayonnaise round it into something creamy enough to coat a spoon.

The fish sauce is the move most home cooks skip, and they shouldn’t. Two teaspoons disappear into the sauce but leave behind a savory backbone that pulls everything forward. Anchovy paste does the same job if that’s what’s in your fridge.

Tarragon and lemon juice keep the flavor bright and a little anise-leaning, which is why this sauce loves salmon, trout, and any white fish off the grill. It also doubles as a dip for crudités or a smear for cold roast chicken sandwiches.

Kitchen Tips

• Pack the watercress firmly when measuring. Loose leaves give a thin, watery sauce.
• Blend everything except the fish sauce first, then add it to taste so you can dial in saltiness.
• Make the sauce a few hours ahead. The garlic mellows and the tarragon blooms after a rest in the fridge.
• Use full-fat Greek yogurt instead of nonfat for a richer, more spoonable texture.

Variations

• Swap watercress for arugula or baby spinach if watercress is hard to find.
• Add a peeled avocado for a thicker, dressing-style sauce that works on grain bowls.
• Stir in chopped fresh dill for a sauce that leans Scandinavian, especially with salmon.