Heat a large heavy skillet, preferably cast iron, over high heat for 2 minutes until it is very hot. Add the corn in a single layer and do not stir. Let it sit undisturbed for 2 to 3 minutes until you see dark brown spots on the kernels. Toss once, let it sit for another minute, then transfer to a plate to cool. The goal is some charred edges, not just warm corn.

Halve the avocados, remove the pits, and scoop the flesh into a large bowl. Add the lime juice right away to slow browning. Mash with a fork to your preferred texture. Some people like it completely smooth and some like chunky pieces throughout. Either way works here.

Add the diced red onion, minced jalapeno, and cilantro to the bowl. Stir to combine. The onion and jalapeno should be distributed throughout rather than sitting in one spot.

Fold in the charred corn and the cumin if you are using it. Stir gently so the corn stays visible and does not just disappear into the mash.

Add the salt and stir. Now add the crumbled cotija and fold it in. Taste the guacamole before adding any more salt because cotija is already quite salty. Adjust lime juice and salt to your liking.

Transfer to a serving bowl and scatter a little extra cotija on top. Press plastic wrap directly onto the surface if you are not serving immediately. Serve with tortilla chips.