Zippy Salsa Tonnato (Cold Tuna Sauce)

1. 1

   Heat the olive oil and 2 tablespoons of the butter in a skillet or saucier. Add onion, fennel, and radishes, and saute on medium-low heat until tender and translucent. Add hot pepper flakes, garlic, and anchovies and continue sauteing over medium-low, until the anchovies have dissolved, and then stir in the tuna, mashing with the back of a wooden spoon to break up any large chunks. Raise the heat to high and add the wine. Cook until almost all evaporated, then lower the heat and stir in the capers and parsley. Swirl in the remaining 1 tablespoon of butter and remove from heat.

2. 2

   Allow to cool slightly, then transfer to a blender or food processor. Add the mayonnaise (or aioli), vinegar (or lemon juice), reserved tuna oil, and water, and process until smooth. Then let it go some more, until it is super light and airy. (You can also do this directly in the pan with an immersion blender.) Adjust for salt, pepper, acid, and-if you prefer a little extra zip-hot pepper. You may need to add a little more olive oil or water if the puree is too thick. Serve as a dip, or tossed with pasta and a little pasta water (and something assertive and green, like arugula), or as a crostini topping, garnished with chopped parsley. [Editors' note: We spread the tonnato on a plate, then topped it with boiled potatoes, blanched asparagus and snap peas, and raw radishes and Romanesco.]

* Per serving · 4 servings · Values may vary.