For the Salsify Bisque:
Peel salsify and soak in water to prevent oxidization. Heat olive oil over medium-high heat in a sauté pan. Cut salsify into batons, reserving a few for garnish, and sauté with thyme. Add shallots, leeks, onions, celery, and parsnip to the pan and cook until tender. Season with salt and white pepper, and add enough water to cover. Purée the vegetable-water mixture in a blender, adding some extra virgin olive oil to emulsify. Pass the purée through a small china cap. Reserve warm.
To Assemble and Serve:
Heat olive oil over medium-high heat in a sauté pan, and sauté oyster mushrooms and shallots. Deglaze the pan with Madeira and toss in the reserved salsify batons. Season with salt and pepper. Put the mushroom-salsify mixture in a ring in the middle of the bowl. Top the mixture with 4 to 5 cubes of foie gras torchon and fried salsify strips. Pour the bisque over the vegetables tableside.