Butter can be frozen in its original store packaging if it is well-wrapped. For longer storage (over 3 months), overwrap the original packaging with foil or place in a freezer bag to prevent absorption of freezer odors.
Simply place wrapped butter in the freezer. It requires no special preparation. For baking convenience, some people pre-cut a pound of butter into tablespoon-sized pieces, flash freeze on a sheet pan, and bag the pieces — this lets you grab exact measurements without waiting for a full stick to thaw.
For compound butter (herb butter, garlic butter): roll the prepared butter into a log using plastic wrap, twist the ends tight, and freeze. Slice off rounds as needed directly from frozen.
6 to 9 months (unsalted). Up to 12 months (salted — the salt acts as a preservative).
Thaw in the refrigerator overnight. For baking where cold butter is needed (pie crust, biscuits), use directly from frozen — grate it on a box grater for quick incorporation.