Peel and clean the cardoons. Set aside in cold water to cover with the lemon juice.

In a heavy saucepan, reduce the cream by half over moderate heat. While the cream reduces, cook the cardoons in salted boiling water until tender. Drain and keep warm.

Strain the oyster liquor into the reduced cream and reduce the mixture by one-third to about 2½ cups. Add the cayenne. Poach the oysters in the cream for 3 minutes.

Off the heat, stir in the file gumbo powder or add a pinch to each serving at the table. Drain the cardoons thoroughly and arrange them on a heated deep platter. Pour the oysters and cream over the cardoons. Serve in heated soup plates.