Torta Ahogada - Rick Bayless

Ingredients

• 1 medium white onion, thinly sliced (divided use)
• 2/3 cup vinegar (any light vinegar will do) (divided use)
• 1/2 teaspoon dried Mexican oregano,
• Salt
• 1 15 ounce can tomatoes (preferably fire-roasted) (divided use)
• 2 tablespoons vegetable or olive oil
• 8 garlic cloves, peeled, whole (divided use)
• 3 1/2 cups chicken broth
• 10 árbol chiles , stemmed
• About 2/3 cup cooked beans (any color is welcome here) with just enough liquid to cover, canned or home-cooked
• 1 or 2 tablespoons fresh-rendered pork lard or vegetable oil
• 4 birote rolls or 8-inch demi-baguettes
• About 1 pound carnitas (homemade or bought from a grocery or taqueria that makes carnitas), warm