Heat 1 tablespoon oil in a 12-inch skillet over medium-high heat. Spread corn kernels in an even layer and let them sit without stirring for 2–3 minutes to develop charred spots. Toss and repeat until you have scattered browning but kernels are not burned. Remove half the kernels to the slow cooker and reserve the rest.

In the same skillet, reduce heat to medium and add 2 tablespoons butter or oil. Sauté the diced onion 4–6 minutes until translucent, then add minced garlic, cumin, smoked paprika, and chili powder and cook 30–45 seconds until fragrant. Pour in 1 cup of the broth to deglaze and scrape up browned bits.

Pour the skillet mixture into the slow cooker. Add the remaining broth, diced red bell pepper, the rest of the charred corn, and 1 bay leaf. Cover and cook on LOW for 2½ to 3 hours or on HIGH for 1½ to 2 hours, until the aromatics are soft and flavors have melded.

Remove and discard the bay leaf. Use an immersion blender to puree about one-third to one-half of the soup until slightly thickened, leaving plenty of whole kernels for texture. If you prefer a thicker broth, whisk 1 tablespoon cornstarch with 2 tablespoons cold water and stir it into the hot soup, simmering for 4–5 minutes until slightly thickened.

Stir in 1/2 cup Mexican crema or sour cream (or Greek yogurt off heat), lime zest and juice, and 1/2 cup chopped cilantro. Season with salt and pepper to taste.

Ladle soup into bowls and garnish with crumbled cotija, diced jalapeño, or chopped green onions if desired. Serve with warm corn tortillas or crusty bread.

Refrigerate leftovers in airtight containers for up to 4 days. To reheat, warm gently on the stovetop over medium-low, adding a splash of broth if needed; add fresh lime and cilantro after reheating.