1. Harmonize this melody in minor 64 chords (they consist of perfect 4th and a minor 3rd) in the right hand.
2. In the bass try playing the long pedal points on the main notes of the D minor scale (D, F, A, G etc.)
3. In the left hand use the same note as in the pedals one octave higher plus an open fifth sound (DAD or FCF etc.)
4. Feel free to change the chords and the pedal points at any rest sign.
Here is the PDF file for printing out this theme.
Of course, this is not really the style of Langlais. It's everyone's style because the techniques and the chords are here for anybody who cares enough and are curious to experiment.