In USA folk say butter is not the same. First it's salted and unsalted, second... the taste is different, it behaves in baking different... why?
American butter is made of cream, European style butter however is made from aged (aka sour cream), and them comes USA pasteurized milk and Europe - not necessary. Then what do cows eat, are they grass fed.
Can you make your own butter? It's quite easy actually. Here is video about America style butter made at home with kitchen stand mixer.
All one does is : beat the cream until solids and butter milk separate
Also this one makes sour cream at home using butter milk. In USA organic milk is the best bet.
Now Russian style: from fresh milk she takes tops - cream, and she will make butter from cream, shaking a lot, long time.
It's important to have it at about 20C degrees, if it's hotter the butter will be too runny, if it's too cold - that will be too hard to beat it. 1/2 to 1/3 of the jar has to be empty.
And shake it... 10-15 min.
Use the same principle using the mixer. at 20C is the best.
In 5-10 min there will be a bit of solids.
Beating cream from sour cream - that's Russian style. Sour cream was sitting in the fridge several days. And here comes the drill. very effective :)
See how much solids? that sour cream was already separated, meaning strained.
They have gadgets for that
Sometimes there is reference about cultured butter
This video has important note about ultra pasteurized and pasteurized cream. the process will not work with that. This is similar to Russian style butter referenced in video 4)