Riddonkulous

I sleep beneath the soil where nobody can see Growing in darkness quite happily I start out small but can feed a crowd And when I am cooked I make people proud I can be baked until my skin turns crisp Or mashed up soft with a buttery twist Drop me in oil and I become a fry Cut me into pieces and watch them disappear nearby I wear a rough little coat of brown But peel it away and there is gold underneath I may look plain and humble at first Yet kitchens around the world know my worth