2 teaspoons olive oil
1/2 cup minced white onion
1 clove garlic, minced
1/2 cup mild-to-medium-hot chile powder
2 cups vegetable broth or chicken broth
1 cup water
1/2 teaspoon dried oregano, preferably Mexican
1 15-ounce container pinto beans, rinsed and mashed, or refried beans
2 tablespoons plain yogurt
12 6-inch corn tortillas, blue corn if available
2 cups shredded sharp Cheddar cheese, (8 ounces), divided
1/4 cup minced white onion, plus more for garnish
To prepare sauce: Heat oil in a medium saucepan over medium heat. Add 1/2 cup onion; cook, stirring, until it begins to soften, about 1 minute. Stir in garlic and continue cooking until the onion is translucent and soft, about 2 minutes more. Stir in chile powder. Add broth, water, oregano and salt. Bring to a boil. Reduce heat to a simmer and cook until thickened and reduced by about one-third, about 20 minutes. (The sauce should be thick enough to coat a spoon lightly.)
To prepare enchiladas: Preheat oven to 400°F. Coat a 7-by-11-inch (or similar-size 2-quart) baking dish with cooking spray.
Combine beans and yogurt in a small bowl.
Spread about 1/4 cup of the sauce in the baking dish. Arrange 4 tortillas in the dish, overlapping them to cover the bottom. Top with half the bean mixture, using the back of a spoon to spread it thin. Scatter 2/3 cup cheese and 2 tablespoons onion on top of the beans. Top with one-third of the remaining sauce, 4 tortillas, the remaining bean mixture, 2/3 cup cheese and the remaining 2 tablespoons onion. Spread half of the remaining sauce on top and cover with the remaining 4 tortillas. Top with the remaining sauce and the remaining 2/3 cup cheese.
Bake the enchiladas until hot and bubbling, 15 to 20 minutes. Let stand for 5 minutes before serving. Serve with additional minced onion, if desired.