If you are using frozen corn, spread the kernels on a clean kitchen towel or a layer of paper towels and press them as dry as you can. Extra moisture is the enemy of a good char, so do not skip this step.

Place a 10 or 12 inch cast iron skillet over high heat. Let it preheat for a full 2 minutes with nothing in it. You want the pan genuinely hot before the corn goes in, which is what creates the charred spots quickly.

Add the corn in a single layer (no oil, no butter yet). Let it cook without stirring for 2 minutes. You should hear it sizzling aggressively. Check the bottom of the kernels for dark brown or black blistered spots, then stir and let it sit for another 1 to 2 minutes. The goal is some kernels charred and others golden, not uniformly browned.

Reduce the heat to medium and add the butter. Stir until it melts and coats the corn, about 30 seconds. Add the lime juice, salt, and black pepper, and stir everything together. Taste and add more salt if needed.

Pour the corn into a serving bowl or onto a platter. Scatter the crumbled cotija evenly over the top and finish with fresh cilantro if using. Serve immediately while it is still warm.