Melt the butter in a large pan over medium heat. Add the shallots and a pinch of salt and saute until soft, 3 to 5 minutes.
Stir in the greens and another pinch of salt. Cover and turn heat down to low; let steam for 5 minutes.
Add the cream and slowly massage it into the greens with a wooden spoon. Cook uncovered until the stems are tender, another 5 minutes. Add the nutmeg. Taste and adjust the seasoning with more salt or pepper, if needed.