Source: NPR, November 29, 2006
3 large celery roots, peeled and cubed
2 Idaho potatoes, peeled and cubed
1 pint light cream
2 tablespoons butter (1/4 stick)
2 tablespoons salt
2 tablespoons truffle oil (optional if unavailable)
2 crisp apples, cored, peeled and diced fine 
1/4 cup all-purpose flour
1/2 cup vegetable oil
Boil cubed celery root and potato in a large covered pot until soft. Drain thoroughly and return to pot. Add cream, butter, salt and truffle oil, and mash and whip until integrated and smooth. 
Dredge the diced apple in the flour. Add 1/2 cup of oil to a saute pan and heat over high heat until smoking. Add apple bits and “flash” fry (quickly over high heat) until crisp, about 2 minutes. Drain on paper towels. 
To serve, reheat the mashed celeriac until warmed through, transfer to a bowl and sprinkle the apple bits over the top.