Place the potatoes in a very large pot. Add 2 gallons of water and the Old Bay seasoning or Cajun spice. Bring to a boil. Add the crabs and return to boil. Boil for 6 to 7 minutes. Add the corn to the pot, return to a boil and cook 2 minutes. Drain, and then arrange the potatoes, crab, and corn on a large platter. Garnish with lemon wedges. Serve with small pots of melted butter for dipping the crab, if desired.
Note: Old Bay seasoning is available in the seafood department or the bottled spice aisle. Cajun spice is available in the bottled spice aisle.
Recipe Options: Make a lobster boil by replacing the crab with four, one pound live lobsters. If you don't want the corn and potatoes to be infused with the flavour of the crab and spice, cook those vegetables separately and then serve them alongside the crab once it's been boiled.