Step 1

For the seafood boil: Heat the oil in a 10-quart or larger stockpot over medium-high heat until shimmering. Add the lemongrass, then the ginger, garlic and onion cut-sides down. Lower the heat to medium and cook until the garlic is light golden brown, about 5 minutes. Add 4 quarts (16 cups) water, increase the heat to high, cover and bring to a boil, 10 to 15 minutes.

Step 2

Reduce the heat to medium to maintain a simmer. Squeeze the juice from the orange halves into the pot, then add the orange halves with the potatoes, sausage, seafood seasoning, fish sauce and corn. Simmer, uncovered, until the potatoes are fork-tender, about 15 minutes. Transfer the potatoes, sausage and corn to a large serving platter with tongs or a slotted spoon; keep the liquid in the pot.

Step 3

Add the clams, crab legs and mushrooms to the pot, then cover and simmer until the clams start to open, about 5 minutes. Turn off the heat, then add the shrimp, submerging them in the liquid. Cover and allow the shrimp to cook in the residual heat until pink, about 3 minutes.

Step 4

Transfer the seafood and mushrooms with a slotted spoon or tongs to the platter with the vegetables and sausage.

Step 5

For the lemongrass-garlic butter: Meanwhile, melt the butter in a saucepan over medium-low heat. Add the lemongrass and simmer to soften, 4 to 5 minutes; scrape off any foam from the top of the butter. Add the seafood seasoning, ground ginger and garlic and cook until the garlic is lightly browned around the edges, about 2 minutes. Whisk vigorously or process with an immersion blender to break down the lemongrass and garlic even more. Turn off the heat, add the fish sauce and lime juice and stir to incorporate.

Step 6

Scatter the eggs, if using, over top of the seafood, sausage and vegetables on the serving platter. To serve, squeeze the lemons over the seafood and toss with some of the lemongrass-garlic butter. Serve the remaining lemongrass-garlic butter on the side for spooning or dipping.