Soak the corn, husks and all, in water for 30 minutes to an hour while you prepare your grill. You’ll want a medium-hot grill (350-400ºF) set up for direct heat cooking.
Mix the crema or mayonnaise in a small bowl with the lime juice, a tablespoon of the cotija, and a little salt. Refrigerate.
Grill the corn for 10 minutes on each side, turn once.
Remove (replace the grill cover to keep the heat in) and quickly strip away most of the husks. Leave one or two layers of corn husk and don’t worry about the corn silk. That comes off later.
Place the near-naked ears back on the grill for 5 more minutes on each side.
Now husk completely. The silk should fall away easily.
Brush the corn with the creamy lime sauce, sprinkle with cheese and chili powder or Tajín and serve hot. It’s even delicious at room temperature, so don’t worry too much about serving time.