Preheat oven to 400°. Toast saffron threads in a small skillet over high heat for 1 minute. Crumble saffron into chicken stock in a saucepan, and bring to a simmer over medium heat.
Rub potatoes with softened butter. Sprinkle with salt and pepper.
Arrange potatoes in one layer in a baking pan and pour the hot stock over potatoes. Roast until tender, about 30–45 minutes. Serve garnished with chopped fresh parsley.