Chiles Rellenos Sauce

Source: Elena's Secrets of Mexican Cooking - Elena Zelayeta

1 onion
2 tablespoons oil
4 cups chicken broth
1 teaspoon black pepper
2 cloves garlic
2 cups tomato
1 teaspoon salt
1 tablespoon Mexican oregano

Chop onion and crush garlic. Cook in oil until wilted. Add tomatoes and press through strainer. Mix with broth and bring to a boil. Season to taste with salt, pepper and oregano. Heat the chiles in boiling sauce for about five minutes.