Preheat oven to 400°. Toss all the ingredients together until the yams are evenly coated on a parchment paper lined baking sheet. Spread the yams out and tuck as much of the rosemary underneath them as possible, this will infuse their flavour but keep them from burning too quickly. Bake for 40 minutes, stirring gently halfway through so they brown evenly. Remove rosemary and serve hot, with another sprinkle of salt and pepper if needed.
Recipe by Love from the Land at https://www.lovefromtheland.com/sumac-rosemary-garlic-roasted-yams/