Preheat oven to 425 degrees F. Trim tops from carrots; thoroughly rinse and dry. Strip the leaves from the stems and measure 2 cups loosely packed leaves; discard stems. Place carrot tops in a food processor with the basil, cheese, pine nuts, garlic, and 1/4 teaspoon salt. With food processor running, drizzle in the 1/3 cup oil in a stream until pureed and smooth, scraping sides as needed; set aside.
Peel carrots. In a 15x10x1-inch baking pan toss carrots with 2 tablespoons olive oil and 1/2 teaspoon each salt and pepper. Roast for 25 minutes or until tender. Top roasted carrots with pesto. Store any remaining pesto in an airtight container in the refrigerator up to 1 week.