It seems we are all in agreement that you have butter.
Susan: "Oh, no. It's the stalker again."
Karen: "You have a stalker?"
Susan: "Yeah, a breakfast stalker, always trying to steal my butter."
The breakfast stalker: gets uncomfortably close "You have butter."
'You are having butter', not accepted!
"to have" in the sense "own, possess" is not usually used in the continuous aspect in English.
"You are having butter" would mean not "You possess butter" but rather "You are eating butter", so that is not a correct translation of Du hast Butter.
Ok, thanks. I thought the sentence meant that someone was having butter ( rather than margarine) on their toast.
Yes; the German cannot mean that.
(That could be Du nimmst Butter, literally "you take butter", but not Du hast Butter which would only refer to possession.)
As ever, many thanks for your so helpful explanations.