Step 1

Combine lime juice, sour cream, mayonnaise, serrano(s), and ¼ teaspoon salt in large bowl. Set aside.

Step 2

Heat 1 tablespoon oil in 12-inch nonstick skillet over high heat until shimmering. Add half of corn and spread into even layer. Sprinkle with ¼ teaspoon salt. Cover and cook, without stirring, until corn touching skillet is charred, about 3 minutes. Remove skillet from heat and let stand, covered, for 15 seconds, until any popping subsides. Transfer corn to bowl with sour cream mixture. Repeat with 1 tablespoon oil, ¼ teaspoon salt, and remaining corn.

Step 3

Return now-empty skillet to medium heat and add remaining 1 teaspoon oil, garlic, and chili powder. Cook, stirring constantly, until fragrant, about 30 seconds. Transfer garlic mixture to bowl with corn mixture and toss to combine. Let cool for at least 15 minutes.

Step 4

Add cotija, cilantro, and scallions and toss to combine. Season salad with salt and up to 1 tablespoon extra lime juice to taste. Serve.