Seafood Boil with Cajun Garlic Butter

Steps

1. Scrub the baby potatoes under running water without peeling them. Cut each ear of corn into 4 pieces with a heavy knife. Slice the andouille into thick 1 1/4 inch (3 cm) rounds. Scrape the mussels, pull off the beards and discard any that stay open after a firm tap on the counter. Rinse the shrimp and keep them cold; to devein them, snip down the back through the shell with kitchen shears and pull out the dark vein.
2. Pour the water into a very large stockpot (at least 12 quarts). Add the Old Bay, kosher salt and bay leaves. Halve 2 lemons, squeeze them over the pot and drop the halves in. Cut the head of garlic in half crosswise and the onion into quarters, skins on, and add them. Bring to a boil, covered, then boil for 10 minutes so the broth absorbs the aromatics. Taste: it should be boldly salty and spicy, like seasoned seawater.
3. Add the potatoes to the boiling broth. Once it returns to a boil, cook for 10 minutes at a steady boil with the lid slightly ajar.
4. Add the andouille and corn. Boil for 7 to 8 minutes, until a knife tip slides into the center of the largest potato with no resistance and the corn kernels are bright yellow and glossy.
5. Meanwhile, make the Cajun butter. Melt the butter over low heat in a small saucepan. Add the finely minced garlic and let it bubble gently in the butter for 2 minutes without browning. Add the Cajun seasoning, smoked paprika and cayenne, stir for 30 seconds, then take it off the heat. Stir in the juice of half of the remaining lemon and half of the chopped parsley.
6. Bring the broth back to a rolling boil, add the mussels, cover and cook for 3 minutes, until the shells open.
7. Turn off the heat. Immediately add the shrimp, push them under the surface with a spider, cover and let them cook in the residual heat for 3 to 4 minutes. They are done when pink, opaque all the way through and curled into a loose C; a tight O means overcooked.
8. Drain everything in a large colander or lift it out with the spider. Discard any mussels that stayed closed, along with the garlic, onion and lemon halves.
9. Tip the seafood, andouille, corn and potatoes into a large bowl, pour over half of the Cajun butter and toss gently to coat. Spill everything onto a platter or a table lined with kraft paper, drizzle with the rest of the butter, scatter the remaining parsley and set the last lemon half, cut into wedges, around it. Serve right away, with bowls for the shells.