Preheat oven to 425F. In a shallow baking pan, toss together the diced potatoes, melted butter and one tablespoon chopped fresh sage. Arrange in a single layer on the pan and roast 20 minutes, or until tender, stirring once. Meanwhile combine remaining sage, garlic and lemon zest in a small bowl to make gremolata. Sprinkle gremolata over potatoes just before serving.