I make butter in a very simple and weird way.
I buy some cream, let it go at least a week past expiration in the fridge, then open the container and let it sit another week or so in the fridge. Once I feel it is going sour (cultured), then I take it out of the fridge and let it sit on the counter for several hours. I taste it. Yep, I taste it. If it isn't sour enough, then I let it sit out over night and taste it again. Some ultra-pastuerized cream can literally sit out for days without going sour. That is kind of scary.
(FYI, right now I have three containers of cream in varying states of decay in the fridge.)
After that I just put the soured cream in a mason jar and shake away until I have butter fat separation. Letting the milk go sour gives a nice tang to the butter (like in the old days). Once the butter fat and butter milk have been separated, drain it out (shaking and draining a few times), and then put it in a bowl and work it with a wooden spoon, making sure to drain the remnant buttermilk out several times. If you don't do this, it will spoil quicker.
The last step is adding flavor. I usually just lightly salt it (kosher or cheese making salt) and mix it in. Sometimes I add herbs or fresh ground pepper.
I also have a vintage wooden butter mold that I use for the leftovers. I form what's left into cakes, freeze it, then wrap in wax paper for later.
k.