Preheat oven to 350 degrees. Combine chestnuts, butter, sugar and salt; toss to coat evenly. Spread onto a greased baking sheet and bake for 10 mins, stir and bake 10 mins more. Let them cool, then break them apart into 3-4 large pieces each.

Spread cubed bread evenly on a baking sheet and bake for 10 minutes at 350 degrees or until slightly toasted. Keep oven on. Cool bread and place in a large bowl.

Melt ½ stick butter in a wide, heavy skillet over medium heat and add leeks, shallots, celery root, sage and thyme, seasoning with pepper. Cook until celery root is tender, about 7 minutes. Add apples and cook until fork tender, then add mixture to bread.

Wipe pan, turn heat to medium high. Add 2 tablespoons butter and mushrooms. Season with salt and pepper and cook 6 to 8 minutes, stirring occasionally, until mushrooms release their liquid and most of it has evaporated.

Add Madeira and cook for 2 to 3 minutes, scraping up any browned bits in pan. Add mushrooms and chestnuts to bread mixture.

In a saucepan, bring stock and currants to a boil; pour over bread mixture and mix thoroughly. Mix in ¼ cup truffle butter, the parsley and chervil. Add a little more pepper, and more salt if necessary.

Increase oven heat to 375 degrees. Place mixture into a greased 9-by-13-inch baking dish, dot with remaining truffle butter and bake for 30 minutes, or until top layer is slightly brown and crisp.