SERVES 4 TO 6
8 tablespoons (1 stick) unsalted butter
1 medium onions, grated on the large holes of a box
grater (about ¾ cup)
1 large clove garlic, minced or grated on a Microplane
(about 2 teaspoons)
½ teaspoon dried oregano
Kosher salt
2 chipotle chiles in adobo sauce, finely chopped