Charred-Scallion Sour Cream

Our neighborhood is full of taquerías where you can order cebollitas—charred scallions—as an accompaniment to your tacos. We use them often to add a pungent and smoky element to dishes. Jason Fox instructed his cooks to grill scallions until they’re “as black as your soul” before blending them into a vinaigrette. We mixed them with sour cream and aioli to top our King Trumpet sandwich, served on a homemade flatbread with mushro