Blanching is a process of parboiling, either to cook further at another time or to cook fully and then to store in the refrigerator until serving that particular vegetable, chilled.
To blanch vegetables: Bring a large (8-quart) pot of water to boil. (I prefer to use one with a built in strainer). When blanching several different vegetables, get them all trimmed and cut into the sizes that you want. For asparagus, rinse them, tied in bunches (rinse the tops extra well). Cut bunches where the woody bottoms meet the tenderer, green stalk. (I rarely peel green asparagus unless they are very large. If doing this, starting at where the bottom of the flowered top meets the shaft, run the blade of a vegetable peeler down the trimmed stalk of asparagus, until you reach the bottom. I always peel white asparagus. When done, tie them all in bunches, using kitchen twine.)
When blanching different vegetables, using the same water, you’ll want to go from the least to the most aromatic (i.e. green beans, snap peas, carrots, cauliflower, asparagus, broccoli, Brussels sprouts). Before adding the vegetables to the water, add a nice dose of salt. While each type of vegetables parboil (uncovered), have a fresh bowl of ice water near your stove. After the vegetables have softened to a crisp-tender stage, remove them from the boiling water and immediately plunge them into the bowl of ice water. Use your hands to swish the vegetables around, helping to facilitate the halting of the cooking process. Lift the vegetables out of the ice water and drain them on doubled paper towels. Pat dry and put in a heavy-duty plastic freezer bag, lined with paper towels, and store in the refrigerator for up to 3 days before enjoying the vegetables chilled, either with vinaigrette or a dip or, sauté the vegetables or cook them further in broth and then puree them for soups.
General guidelines for parboiling vegetables: All timing depends on the girth and overall age and condition of the vegetable. Add 2 to 3 more minutes for those vegetables that you plan on eating chilled, without further cooking.
Asparagus: 3 to 6 minutes (8 to 10 for white asparagus)
Green beans: 3 to 5 minutes
Broccoli: 3 to 5 minutes
Carrots: 5 to 10 minutes (depending on their girth, the size of their inner core and the thickness of the slices; 6 to 8 is the usual time requirement)
Cauliflower: 3 to 5 minutes
Brussels sprouts: 3 to 5 minutes (3 if halved, 5 if left whole)