I used to have Nubians; loved them and really miss them. As soon as I'm retired I'm getting some more (crazy work schedule will not allow dairy animals right now). Nubians have the highest butterfat content of all dairy goats tho of course it varies by individual. What I used to do was I strained milk into quart jars and put right into the refrigerator. I noticed if it wasn't moved for two or three days there would be a fine skim of cream on the top. I bent a spoon handle so it was 90 degrees to the bowl and would skim off the two or three tablespoons per quart and put it in a container in the freezer.
Then for special holidays I would have enough to make whipped cream for our pie. Never really got enough that way to make butter tho.

This is a video of someone doing it the way you mentioned, without a separator.
I don't pasturize the milk, would that make a difference? The girl in the video does.