Position rack in upper third of oven; preheat to 500°F.
Toss potatoes, butter, oil, rosemary, salt and pepper in a large bowl until evenly coated. Arrange in a single layer in a 9-by-13-inch metal baking pan (do not use a glass dish). Roast, flipping once, until browned, about 30 minutes.
Combine broth, vinegar and honey in a small bowl. Carefully add the broth mixture to the pan. Continue roasting, undisturbed, until the potatoes are very tender, most of the liquid is absorbed, and the vinegar has thickened slightly, 12 to 14 minutes. Recipe developed by Jasmine Smith
