Gather all ingredients. Preheat a large cast-iron skillet over medium-high heat until hot, about 5 minutes.
Coat corn evenly with oil. Add corn to skillet; cook over medium-high, turning occasionally, until tender and lightly charred, 12 to 15 minutes. (Alternatively, preheat a gas grill to High [450 to 500 degrees F (230 to 260 degrees C)]. Place corn on oiled grill grates; grill, uncovered, rotating every few minutes until charred all over, about 10 minutes.) Transfer corn cobs to a cutting board and let cool 5 minutes.
Meanwhile, combine herbs, mayonnaise, sour cream, mustard, garlic, 2 tablespoons of the lemon juice, 1/2 teaspoon of the pepper, and 1/4 teaspoon of the salt in a blender; process until smooth and a very light green color, scraping down sides as needed, about 1 minute.
Cut kernels from corn; discard cobs, and place in a large bowl with avocado, shallot, remaining 1 tablespoon lemon juice, 1/4 teaspoon pepper, and 1/4 teaspoon salt, and toss to combine.
Pour 1/3 cup dressing over corn mixture and toss until evenly coated; garnish with additional fresh herbs and cotija. Save remaining dressing for another use. Recipe developed by Amanda Holstein
