Tomatillo Sauce (Salsa Verde)

Place tomatillos and chiles in a saucepan; add water to cover. Bring to a boil and simmer until tomatillos are very tender, about 15 minutes. Drain.

Pulse onion and garlic in a food processor until finely chopped. Add the drained tomatillos and chiles and process until smooth. Heat oil in a large saucepan over medium-low heat. Add the tomatillo mixture and oregano. Cook, stirring constantly, until the mixture darkens and thickens, about 10 minutes. Stir in broth and return to a simmer. Simmer, stirring occasionally, until the sauce is thick enough to coat the back of a spoon, about 20 minutes. Season with salt and let cool to room temperature.