Funny stuff, parsley. Tastes really rather bland, buts adds an indefinable zing to loads of dishes. And totally useless dried.
When I was a kid, Mum would sometimes have way too much parsley, so she’d chop it, mix it with water and pour the resulting goo into an ice-cube tray. Once the cubes were done, she’d shove them into a plastic bag, et voilà, teaspoon sized portions of parsley ready to go. That was the theory. The reality was that getting the springy, bouncy parsley leaves into the ice cube tray was harder than it sounds, no matter how finely chopped they were.
The simple approach is to chop up a bunch of parsley, and simply stuff into a rectangular plastic “sandwich bag”, and put that into the freezer. The trick here is, once the bag is sealed, to squish it around the contents are evenly spread and the bag is almost flat. This way you can easily snap off a corner.
Same thing works for leftover mash, too. The flatter you squish it, the easier it is to stack in the freezer and the quicker it is to defrost. (I try and make my frozen slabs of mash line up with the dish in which I make Shepherds’ Pie…)