Fill a large pot with water
Leave enough room at the top so it won't overflow once the food you're blanching is added.
Place the food in a steamer insert
If you don't have one, consider using a strainer, or have a perforated utensil ready for fishing out the food once boiled.
Add a generous amount of salt to the boiling water
I use kosher salt, but any type is fine.
Make an ice bath
Fill a bowl (be sure it's large enough to hold the steamer insert later) with ice and enough water to cover it. Set aside.
Once the water is at a full rolling boil
Add the food. Be sure it's fully submerged. Keep the heat high so the water temperature drops as little as possible.
Watch for changes in color
This should happen almost instantly, as in the case with this broccoli. Once the food brightens, keep testing its texture for desired doneness.
Shock the food in the icy water
Let sit for several minutes until it no longer feels warm. Strain; use as desired.