Rinse the broccoli, and slice the florets from the stalk. You want small, even-sized pieces, so cut large florets in half.
Take the remaining chunk of stem and remove and discard the dried-out bit at the bottom. Use a knife to remove the tough outer layers and slice the revealed tender stalk into ½ inch (1 cm) disks.
Bring a large pot of water to a boil over high heat. Use enough water to submerge all of the broccoli. Add a tablespoon of salt for each head of broccoli (adding salt is optional).
While you wait for the water to reach a rolling boil, fill a large bowl with cold water and ice.
Add the broccoli florets and sliced stem to the boiling water and cook for two minutes.
Drain the broccoli and immediately place the florets in the bowl of ice water. Let them cool completely, about five minutes.
Transfer the cooled broccoli to a clean kitchen towel and gently pat dry.
Line a baking sheet with parchment paper and arrange the blanched broccoli pieces in a single layer.
Place the tray in the freezer and freeze until solid, about an hour.
Transfer the flash frozen broccoli to an airtight container or freezer bag and return it to the freezer.