Place oven rack in upper third of oven. Preheat oven to 500 degrees F.
In a large bowl, add sliced potatoes, melted vegan butter, oil, chopped rosemary, salt and pepper. Toss together well.
Place potatoes in a single layer on a 9x13 pan. Roast for 15 minutes, turn, cook for another 15 minutes or until browned. **DO NOT USE GLASS DISHES - THEY WILL SHATTER AT THE TEMP.
While cooking, in a bowl whisk together the broth, lemon juice, and garlic. Remove tray from oven. Carefully add broth mixture and rosemary sprig to the pan. Toss together. Add back to oven until most of the liquid has absorbed and potatoes are tender (10-12 minutes).
Remove and top with additional fresh rosemary and lemon zest if desired.