I am partial to “16/20” size shrimp because it’s the perfect “peel and eat” size but use any kind of shrimp you like. 16/20 means there are 16-20 per pound of this size shrimp. You can use the larger “U-10”, meaning there are “under 10” (9 or fewer) pieces per pound. The key to a tender result is cooling the liquid off before adding the shrimp. It’s like easing them into a warm bath instead of plunging them into a boiling one; they will emerge tender. Peel and serve almost room temperature for best results. The sauce is a classic. There are many horseradish products at the store; has to be the smooth “creamed” ones for best results with this sauce.