- 3 large garlic cloves, left unpeeled
- 1 (1/2-inch-thick) slice large white onion
- 1 (3-inch-long) small dried ancho chile (1/4 ounce)
- 1/2 cup water
- 3/4 teaspoon salt
- 1/2 teaspoon dried oregano (preferably Mexican), crumbled
- 2 tablespoons vegetable oil
- 10 ounces mushrooms, trimmed and thinly sliced
- 1 tablespoon tomato paste
- 3 1/2 cups low-sodium chicken broth (28 fluid ounces)
- Heat a dry 12-inch heavy skillet over moderate heat until hot, 3 to 5 minutes. Lightly smash garlic in skins with side of a large knife, then add to skillet along with onion slice and cook, turning over once or twice with tongs, until onion is well browned and garlic is slightly softened, about 8 minutes.
- Meanwhile, discard stem, seeds, and veins from chile and tear chile into 4 pieces. Add chile to onion and garlic in skillet and toast, pressing flat with tongs and turning over occasionally, until chile turns a brighter red, about 1 minute.
- Discard garlic skins and coarsely chop onion, then purée garlic, onion, and chile in a blender with water, salt, and oregano until smooth.
- Heat oil in skillet over high heat until hot but not smoking, then sauté mushrooms, stirring occasionally, until golden and any liquid is evaporated, about 6 minutes. Reduce heat to moderate, then add tomato paste and cook, stirring, 1 minute. Add purée and cook, stirring, 3 minutes. Stir in broth and simmer 5 minutes.