Preheat the oven to 350°F. Slice the plum tomatoes in half and place them skin-side up on a greased baking sheet. Drizzle with 1 tablespoon of olive oil and roast for 35 minutes, until the skins wrinkle and the edges brown.

Meanwhile, heat the remaining olive oil in a large soup pot over medium heat. Sauté the onion, garlic, and bell pepper for about 5 minutes until softened. Stir in the chili powder and cumin, cooking for 1 minute until fragrant. Add the chicken stock, 1 cup of water, and the ancho chile. Bring to a boil, then cover and simmer for 15 minutes until the chile softens.

Once softened, remove the chile from the pot, discard the stem, and remove the seeds if a milder heat level is preferred. In a food processor, blend the softened chile, canned tomatoes with their juices, and roasted tomatoes (including any juices and browned bits) until smooth. Pour this mixture back into the soup and continue simmering, covered, for 1 hour.

Season with salt, pepper, and ground red pepper (if using), then stir in the cooked chicken. If using fresh corn, cut the kernels off the cob and simmer for 5 minutes. If using frozen corn, heat until warmed through.

To serve, ladle the soup into bowls and garnish with avocado slices, tortilla chips, diced tomatoes, cilantro, shredded cheese, and a spoonful of sour cream. For extra heat, blend 1 chipotle pepper with the tomatoes and chile before adding it to the soup. Enjoy!