In a large pot: 4 cups of water, your favorite beer (one on the side for drinking), half a lemon, 2 crushed garlic cloves, Cajun spice mix, Old Bay seasoning.  Bring to a boil and remove from heat.  Place large (preferably 31/35) , shell-on shrimp into pot and let sit for 6-8 minutes (or until shrimp are white and curl into a C shape)

Drain broth and toss shrimp with ice to shock them (which cools them down and also keeps their bright pink color).  Top with more seasoning and serve with lemon wedges, cocktail sauce, and your favorite crisp white wine or beer.