Hi Nam
There are high quality butters on the market, even in the AOC designation, for specific and adapted uses, croissants, puff pastry, etc. The two essential aspects to remember about butter are flavor and technical qualities. In the final flavor of the products, all butters with the same incorporation rate do not have the same flavor. Many of us find that fine and extra fine butters have better flavor results than others. They are also technically more delicate to use in hot climates. The second determining aspect is the technical qualities, machinability, and therefore result and regularity in all seasons. To work a Croissant dough you need the butter to come directly from the cold. , which, when barely worked with a rolling pin or a sheeter, are flexible enough to be pasted directly into the dough, and proceed directly to turning the puff pastry.
For an optimal result, we need a good quality butter, with a fat percentage of 82%. It is the minimum rate for puff pastry. It is more stable to heat, and does not melt as easily, which makes our work easier.
Answering your second question, you can use fresh pasteurized milk.
We hope this information is helpful.
Greetings.