How to Make It
Preheat oven to 450°.
Line a rimmed baking sheet with aluminum foil. Whisk together the lime juice, 2 teaspoons olive oil, ancho chile powder, paprika, and 1/4 teaspoon salt in a small bowl. Place the corn on the prepared baking sheet, and brush with the lime mixture. Roast the corn for 30 minutes.
Remove corn from the oven. Adjust oven rack 4 inches from heat, and turn on broiler. Return corn to oven, and broil, turning, for 3 minutes or until browned in patches.
Whisk together buttermilk, grated Parmesan cheese, and remaining 2 teaspoons olive oil and 1/4 teaspoon salt in a small bowl. With a small, sharp knife, cut corn off cobs into a serving bowl; gently toss kernels with grape halves and mixed greens. Divide salad among 4 dinner plates. Garnish each with flowering herbs, if desired, and drizzle evenly with dressing; serve.