Japanese sweet potatoes have a deep magenta skin and white flesh that turns Champagne gold as it cooks. They're simultaneously drier and creamier than orange-fleshed sweet potatoes, which means that when you roast them at high heat (cubes, wedges, circles, or halves, simply coated with olive oil and salt and cooked between 425 and 450°), their edges get unbelievably crispy and burnished, belying the pudding-like centers. They're so naturally sweet—more of an earthy, chestnut-y sweetness rather than a sugary one—that the only adornment you need is a sprinkle of flaky salt.