Shuck the corn. Remove all shucks and silks, but leave an inch or two of the stalk. You can use it as a handle. Set the corn aside.
Prepare the grill. Start with clean grill grates, then oil the grates while the grill is cold. To make it easy, dip a wadded-up paper towel in cooking oil, making sure it is not dripping. Hold the oil-soaked paper towel with tongs and rub the grates. Preheat the grill to medium-high with the lid shut. Aim for about 400℉.
Grill the corn: Rub the corn with a thin layer of oil. Grill it over medium-high heat for about 10 minutes, turning occasionally. Continue to grill until all sides have a nice layer of char.
Top the street corn. Mix the sour cream and mayonnaise together and rub the grilled ears of corn with a layer of the sour cream/mayo mix. Sprinkle with a generous layer of cotija, coating all sides. Then sprinkle with plenty of Tajin. Top with fresh chopped cilantro and enjoy!
Notes
How to make roasted corn in the oven:
Preheat the oven to 425℉
Shuck the corn as described above, leaving a handle for holding while eating.
Rub the corn with a thin layer of oil, then wrap each ear individually in aluminum foil.
Bake for 20 minutes, flipping over halfway through.