Wash thoroughly and soak in salt water (1 tablespoon salt per quart of water) for 30 minutes to drive out any insects hiding in the florets. Cut into uniform florets about 1 to 1½ inches across. Peel and slice the stems if you want to freeze those too.
Blanch florets in boiling water for 3 minutes (or steam blanch for 5 minutes). Immediately transfer to an ice bath for 3 minutes. Drain very thoroughly — wet broccoli gets icy and clumpy in the freezer.
Flash freeze: spread blanched, drained florets on parchment-lined sheet pans in a single layer. Freeze until solid (1 to 2 hours), then transfer to freezer bags and press out air.
8 to 12 months.
For most uses, cook directly from frozen. Steam, roast, or stir-fry without thawing for the best texture. If adding to casseroles or soups, drop in frozen. Avoid boiling frozen broccoli — it overcooks quickly and becomes mushy.