In a Dutch oven, cook the finely chopped onion and minced garlic in hot vegetable oil over medium-high heat, stirring constantly, until tender.
Add the refried beans and the next 3 ingredients, stirring until smooth; bring to a boil.
Reduce the heat and simmer for 15 minutes.
Stir in cilantro, if desired.
Cut the corn tortillas into thin strips, spread them in a single layer on a baking sheet, and bake at 350°F for 15 minutes or until they are nicely browned, stirring every 5 minutes.
Allow them to cool.
Notes / Tips / Wine Advice:
To serve, ladle the soup into bowls, and top each with tortilla strips, cheese, and a dollop of sour cream. Serve immediately.