Prepare the boil. In a large stockpot over medium-high heat, combine the water and beer (if using). Bring the liquid to a boil. Season the boil with the Cajun seasoning, Old Bay seasoning, and a few dashes of hot sauce- to taste. Add the sliced onion and lemon wedges into the pot. Stir to combine and let the mixture boil for 15 minutes.
- Add the andouille & potatoes into the pot, stirring well. Let the andouille and potatoes cook for 15-20 minutes, until the potatoes are fork-tender.
- Add the seafood & corn. Nestle the snow crab clusters into the pot along with the shrimp and corn on the cob. Continue boiling for another 5-7 minutes, cooking until the shrimp is pink. Meanwhile, make the sauce.
- Make the garlic butter sauce. On a separate burner, in a small saucepan over medium heat, combine the butter, garlic, lemon juice, Old Bay seasoning, parsley, Cajun seasoning, smoked paprika, and hot sauce- to taste. Stir and simmer the sauce until the butter melts and the sauce is well combined, about 5-7 minutes.
- Assemble cajun seafood boil with sauce. Line an extra large baking sheet with newspaper or foil/parchment paper. Use a spider strainer to remove the seafood boil contents from the pot and place onto the prepared baking sheet along with the hard boiled eggs (if using). Pour the garlic butter sauce over the seafood boil ingredients and toss to coat.
- Serve this Cajun seafood boil immediately as-is on the baking sheet or divide the boil onto individual plates to serve if you prefer. Enjoy!