Heat the butter and olive oil together in a large stockpot over medium heat. Once the butter is melted, add the chopped onion and cook until softened, about 5 minutes. Stir in the garlic and cook for 1 more minute, just until fragrant.

Place the chicken into the pot, then add the diced tomatoes, enchilada sauce, black beans, corn, seasonings, and broth. Stir to combine and bring the soup to a boil. Lower the heat and simmer for about 30 minutes, or until the chicken is fully cooked and tender.

Remove the chicken from the pot, shred it with two forks, then return it to the soup.

Turn the heat to low and stir in the cream cheese until smooth and fully melted. Add the shredded cheddar cheese and stir until the soup is creamy.

Top with tortilla strips, sour cream, and fresh cilantro, and serve hot.