Process first 5 ingredients, 2 tablespoons oil, and 1/2 teaspoon salt in a food processor or blender until smooth, stopping to scrape down sides. Set aside.
Toss together halved potatoes, 1/2 teaspoon pepper, remaining 2 tablespoons oil, and remaining 1/2 teaspoon salt in a large bowl; spread potato mixture in a single layer in an aluminum foil-lined 15- x 10-inch jelly-roll pan.
Bake at 425° for 25 minutes or until potatoes are golden brown and tender, stirring after 10 minutes. Toss potatoes with lemon-and-herb mixture until evenly coated.