Bring a pot of water to a boil. Fill a large mixing bowl with ice water.
Prepare the parsnips by scrubbing them clean and peeling them if desired. Trim off the ends and cut them into bite-size pieces.
Drop them into the boiling water and blanch for 2 to 3 minutes. Remove promptly with a slotted spoon and transfer to the bowl with ice water. Let them cool in the water for a few minutes, adding more ice as needed if it starts to melt. Drain the parsnips.
Optional: transfer the parsnips to a single layer on a baking sheet lined with parchment paper or a silicone mat. Place this baking sheet on a flat surface in the freezer (where it won't get bumped). Freeze for a couple of hours until the parsnips are frozen solid. This step will prevent the parsnips from sticking together.
Transfer the frozen parsnips to a freezer bag or container. Seal, label, and store in the freezer. Store for up to 12 months. For the best taste and quality, use them within 6 months.
Use frozen parsnips in soups, casseroles, and other hot dishes. You do not need to thaw them first. You can also roast them from frozen.
Blanching then cooling the parsnips helps maintain their quality and texture. You can skip the blanching process if desired, but the parsnips won't last as long in the freezer and won't taste as good. To freeze parsnips without blanching, clean, trim, and peel them if desired. Slice them into small pieces and transfer to freezer bags or containers. Store for up to 2 months.
Don't use frozen parsnips in dishes that call for raw parsnips. They will get soggy. Stick to cooked recipes.