*If the butter and cream are cold when added to the hot liquid the sauce will separate/split. This can also happen when stored in the fridge for a while.
If your sauce does separate, just reheat it gently while stirring or use a hand/stick immersion blender until it combines again.
This sauce will keep in an airtight jar or container for at least a week or two in the fridge. Just ensure you have used fresh cream.