Trim the cardoons and cut into 2-inch lengths. Blanch in boiling water acidulated with the lemon juice for 10 minutes, then drain thoroughly.
In a large pan, heat the olive oil and fry the cardoons gently for 5 minutes. Add the olives and truffle, and stir for 1 minute. Sprinkle the flour over this and stir to mix evenly. Stir in the wine and simmer for 10 minutes, stirring occasionally