Slather each ear of corn with crema and sprinkle with cotija. Drizzle with the juice of a lime half, dipped in chile powder.
To make homemade Mexican Crema: combine 1 cup sour cream, 1 cup heavy cream, and 1 teaspoon sea salt in a bowl. Cover with plastic wrap, and let it set at room temperature for 3 hours. Serve at room temperature. (You can store leftover crema in an airtight container in the refrigerator until the expiration date of the sour cream.).