Boil the Base: Fill your big pot with water - enough to cover everything with room to spare. Crank that heat up HIGH and bring it to a hard, rolling boil. Add your halved lemons, quartered onions, whole garlic heads, and potatoes. Let them boil hard for 15-20 minutes until the potatoes are al dente. You want them tender when you stick a fork in, but with just a little resistance - not mushy.
Add Sausage and Mushrooms: Toss in your chunked sausage and mushrooms. Keep that boil going strong for another 5 minutes. The sausage will start releasing its smoky flavor, and the mushrooms will begin soaking up all that good broth.
Add the Shrimp: Here's where timing matters. Gently stir in your well-drained shrimp, making sure they're spread out in the pot. Heat them at least 60 seconds.
The Cool Down (This is Critical!): Turn off the heat and add your frozen corn and ice bag. Stir gently but don't go crazy with it.
Check for Peel-Readiness: After 5-10 minutes, grab a shrimp with your tongs. Carefully try to peel it. If the shell separates easily from the meat and you can see a gap between them, and the meat looks white and opaque (not gray), you're ready for seasoning. If not, add more ice and wait a bit longer.
Season and Soak: Once your water is lukewarm, stir in your Cajun seasoning and those pickled jalapenos. Stir until everything dissolves completely. Do NOT turn the heat back on! Let everything soak for 20-25 minutes minimum. The longer it soaks, the more flavor it picks up. Stir it every now and then.
Drain and Feast: Carefully pour everything into your giant colander. Give it a good shake to get rid of extra liquid. Dump it all onto a big platter or spread newspaper on your table and pile it on. Serve it up right away with some crackers and cold drinks!
