If using fresh corn, cut kernels off cobs. If using frozen, thaw and pat dry with paper towels.
Heat large cast-iron skillet over medium-high heat. Add butter or oil and let it melt. Add corn kernels in an even layer. Cook undisturbed 3 to 4 minutes until charred on bottom.
Stir corn and cook another 3 to 4 minutes, stirring occasionally, until golden-brown bits appear throughout. Remove from heat and let cool 5 minutes.
In large mixing bowl, whisk together mayonnaise, sour cream or crema, cotija cheese, lime juice, chili powder, and smoked paprika until smooth.
Add cooled charred corn, cilantro, and jalapeño (if using) to dressing. Fold together until all corn is coated. Season with salt and black pepper to taste.
Serve immediately or refrigerate at least 30 minutes for flavors to meld. Before serving, garnish with extra cotija cheese, chili powder, and cilantro. Serve with lime wedges.