Take a stick or two of butter, allow it to come to room temperature - you'll want it nice and soft.

Stir in whatever flavoring agents you like (see below), mixing and matching as desired.

I like to go 2-3 tablespoon of solids (fresh herbs, zest, whatever) or around ~1- 1.5 tablespoon of powders per stick of butter, as a rough guide... but there's a lot of room to play.

Make sure to pack a lot of flavor into it (½ teaspoon of, say, curry powder will NOT cut it!).

Also, I try to vary colors to make it look pretty - for instance, mint and cilantro in with the curry powder!

Whip it until everything is well distributed.

Refrigerate for about 10 minutes, or just long enough for it to firm up slightly - but still be workable.

Dump it out onto a section of plastic wrap and roll it into a log. (Alternatively, mush it into an appropriately sized ramekin or other vessel.)

Chill until firmly set.

Try to use the butter within one week, if stored in the fridge. If you'd like to hang on to it for longer than that, it can be stored in the freezer for about a month.