In a large pot of boiling water, squeeze the lemon juice, then stir in the lemon quarters, creole seasoning, 2 tsp cayenne, garlic, potatoes and a few good pinches of salt. Boil about 12 minutes, until the potatoes start to soften.
Add the sliced sausage and boil another 5 minutes.
Then stir in the shrimp and corn, boiling another 3 to 5 minutes. Put your head over that pot for a good creole face steam.
Carefully drain the liquid from the pot, leaving all the goods in it.
In the meantime, whisk together the ketchup, yogurt, ½ tsp remaining cayenne and horseradish in a small bowl. Taste it.
Then dump the boil out on a large table, sprinkle some parsley over the whole shebang and serve with little dipping sauces for everyone.
