Heat the butter or olive oil in a large cast-iron skillet over medium-high heat until hot and bubbling.
Add the corn kernels to the skillet and spread them out into an even layer. Let them cook completely undisturbed for 2 to 3 minutes to develop a dark char.
Stir the corn and spread it out again, repeating the process until the majority of the kernels are beautifully charred (about 8 to 10 minutes total).
Add the minced garlic and diced jalapeño to the skillet. Cook for 1 additional minute until fragrant, then remove the skillet from the heat and allow the mixture to cool slightly.
In a large mixing bowl, whisk together the mayonnaise, sour cream (or crema), fresh lime juice, chili powder, and salt until smooth.
Transfer the warm charred corn mixture into the large bowl with the dressing.
Fold in the crumbled cotija cheese and fresh chopped cilantro, tossing thoroughly until the corn is evenly coated.
Serve warm, at room temperature, or chilled. Garnish with additional crumbled cotija cheese, a light dusting of chili powder, and lime wedges.