In a large skillet over medium-high heat, brown the sausage, stirring, about 6 minutes, then drain on paper towels. Set aside.
Put the potatoes in a large saucepan, add enough water to cover and 1/4 teaspoon of the salt, and bring to a boil. Reduce the heat to medium and simmer until fork-tender, about 12 minutes. Drain and return the potatoes to the saucepan over medium heat to dry for about 2 minutes. Mash the potatoes with a fork, add the andouille and cream, and stir to mix. Stir in the remaining 1/4 teaspoon salt and the black pepper. Keep hot over very low heat.
Make the stew: In a large skillet over medium heat, melt the butter. Add the onion, salt, and black pepper and cook, stirring for 3 minutes. Add the garlic and cream and simmer for 3 minutes. Add the oysters, and their liquor, the parsley, Worcestershire, and hot sauce and cook until the edges of the oysters curl, about 4 minutes.
To serve, spoon equal amounts of the mashed potatoes into small serving bowls and top each with a generous ladleful of the oyster stew. Pass on a tray.
Recipe courtesy of Every Day's a Party, Emeril Lagasse, William Morrow