Wash the parsley and remove all the stems, even b thin ones, so that you're left with the leaves only. (This is easy if you just pull off the leaves with your hands without using a knife.)
Dry the parsley very well, using a salad spinner or paper towels. Make sure to pat dry it really well.
Put the parsley in a plastic zip bag, leaving some air in the bag to start. Freeze for more than an hour. (This helps the parsley become "minced").
After more than an hour has passed (or preferably, leave in the freezer overnight) and the leaves have frozen hard, deflate the bag a bit and squeeze the bag several times to crunch the parsley into fine bits.
Once the parsley is finely crushed, you can freeze it as-is.
You can use it in soups or in omelettes.
Use in Manila Clams with Escargot Butter Recipe ID: 2268999.
Story Behind this Recipe
I wanted to avoid letting parsley go bad if I buy a bunch of it, or let the parsley I grow in my garden die. I've been freezing parsley like this for more than 10 years.
The key is to dry the parsley very, very well. If there's any moisture left on it, you won't get fine and nicely colored parsley bits, it will form clumps in the bag. It's really convenient to store parsley this way, since you can avoid the step of chopping parsley with a knife before adding to your cooking.