Step 1Heat the oven to 325 degrees. In a heavy pot or Dutch oven over medium heat, bring the black beans, water, chiles, onions, garlic and bay leaf to a simmer. Cover tightly and transfer to the oven.
Step 2Cook for 1 hour, then add 1 teaspoon salt and a generous grinding of black pepper and stir to combine. Re-cover the pot and return it to the oven to cook until the beans are tender and creamy, 30 to 45 more minutes.
Step 3Use an immersion blender to coarsely purée the beans just enough to release some of the starch. Alternatively, purée 1 cup of beans in a stand blender and return them to the pot. Heat just until the beans have thickened. (The dish can be prepared to this point several days in advance and refrigerated, tightly sealed.)
Step 4When ready to serve, bring the beans back to a simmer. Add a little more water if they are too thick. Taste and correct seasoning with salt and pepper.
Step 5Ladle the beans into warmed serving bowls and garnish with a spoonful of crema Mexicana, a sprinkling of green onions and cilantro, and grated cotija cheese, with more passed at the table. Serve immediately.