On the stove top, melt the butter over medium heat and add the onions. Saute until the onions are translucent.
Add the cooked onions, chicken broth, black beans, corn, green chiles and chili powder to a 5 qt stock pot.
In a small mixing bowl, whisk the flour and the half-and-half. Add this to the stock pot whisking it in as you add.
Cover and cook on medium heat until the liquid begins to boil. Lower the heat and simmer for an additional 10 minutes.
Add in the shredded cheese and fresh chopped cilantro. Stir until the cheese has melted.
Serve topped with shredded cheese, diced tomatoes or pico de gallo.