Add the potatoes to a saucepan and cover with water. Salt water and bring to a boil. Reduce heat to a simmer and cook until potatoes are tender, about 15 minutes. Drain, return to saucepan to dry potatoes completely. Flatten each potato using your palm (if potatoes aren't too hot) or the flat side of a meat pounder. Serve potatoes on a large platter and spoon creme fraiche on top of potatoes. Top with lime zest and squeeze lime over potatoes. Season, to taste, with salt and pepper.