Heat an inch or so of salted water in a large pot, preferably big enough for the asparagus to lie flat in. If your pot isn’t large enough to fit the asparagus in a horizontal layer, that’s ok, as long as there is enough room for the asparagus to fit into the pot with the lid tightly placed on top.
Once the water has come to a boil, place the asparagus in the pot no more than a few layers deep, and cover the pot. Return the water to a simmer. When the asparagus is cooked to a crisp-tender stage, about 2 minutes for thin spears, and 4 minutes for thicker stalks, drain the asparagus and plunge into the ice bath. When you poke the spears with the tip of a sharp knife, you should feel slight resistance. The color should be bright green. Allow to cool completely in the ice bath.
Drain the asparagus and transfer to a clean dish towel and pat dry. You can then either transfer the asparagus to a freezer-proof bag, press out all the air, label the bag, and freeze; or, if you want to be able to pull out a smaller amount of the stalks at a time, flash-freeze them before transferring to a bag. Place the asparagus in a single layer on a plate or baking sheet and transfer to the freezer. Once they are partially frozen, after about 30 minutes, transfer them to a freezer-proof bag, press out the air, and freeze completely. These will last for up to 8 months in the freezer.
Notes
Cooking asparagus briefly before you freeze it locks in the texture and bright green color of the vegetable (this is true of freezing most vegetables). Blanching simply means quick-cooking a vegetable, and then plunging it into an ice water bath to “shock” the vegetable, e.g., stop the cooking. This also helps the asparagus (or other vegetable) retain its color and texture.
Make sure to use a large pot, preferably big enough for the asparagus to lie flat in, or at least large enough for the asparagus to fit into the pot at an angle with the lid tightly placed on top.
Make sure to have the ice bath ready before you put the asparagus in the boiling water, as the cooking time is very quick.
If you have thick asparagus, you may want to not only trim off the bottom inch of the stem but also peel the tough outer skin on the bottom few inches of the stalk.