Blanch the cabbage: Prepare a large pot of boiling water. Add the cabbage and boil for 30 seconds to 1 minute, until wilted.
Flash freeze: Rinse the cabbage under cold water until cool to the touch. Pat the cabbage dry. Line a rimmed baking sheet with parchment paper, then place the cabbage in a single layer. Flash freeze for 1 hour.
Place the cabbage in an airtight container or freezer-safe plastic bag. If using a bag, use a straw to suck any remaining air out of the bag and seal it.
Mark the “Use by” date. Use a permanent marker to label with a “use by” date that is 3 months in the future.
Freeze. Place the container or bag in the freezer and freeze for up to 3 to 6 months. For best results, use in 3 months. You can use frozen cabbage directly in cooked dishes; no need to thaw (do not use raw).