Cut the corn kernels off the cobs (if using) and measure out 4 cups (if there are any leftover kernels, save them for another use). Reserve cobs.

Melt the butter in a large, heavy bottomed saucepan over medium heat. Add the onions with a pinch of salt and pepper; cook 5 minutes, stirring occasionally, or until light golden and softened. Add the jalapeños, garlic, cumin and oregano and cook 2 minutes, stirring. Stir in the potatoes and cilantro. Add the cobs (if using), along with 6 cups of broth or water; bring to a boil. Lower the heat to a simmer and cook 5-10 minutes. Remove and discard cobs. Add the corn kernels; bring back to a simmer and cook 5 minutes, or until the potatoes and corn are tender.

Working in batches, puree the soup in a blender (you could also use a hand blender—the soup will be slightly chunkier). Be careful when working with hot liquids! Pour the soup back into a saucepan and warm it over medium-low heat. Stir in the lime juice and season to taste with salt and pepper. Add a pinch of sugar if the soup could use some sweetness (particularly if using frozen corn). Do Ahead: The soup can be made up to 2 days in advance, stored in a sealed container in the refrigerator. Reheat and stir well before serving.

Ladle the soup into serving bowls. Garnish each with some shredded chicken, a sprinkle of Cotija or feta cheese and a few cilantro leaves. Serve with lime wedges. Warm, butter-smeared corn bread is a delicious accompaniment.