That’s the one! I have only John Steinbeck’s version of the Arthurian tales, and the only thing I could find close to my memory was the far less inspiring tale of Pelleas, Gawain and Ettarde.
My purpose for this question was that I have been writing a short story for a writing course, and I took it upon myself to try and write a story styled after the chivalric romances with a twist – a young knight takes it upon himself to challenge a veteran warrior for a lady’s hand, and thus goes to his friends for help and advice – but instead of giving him wisdom or magic weapons, they tell him off for his foolishness, until at last he encounters his liege, who forces him to question just how much he actually wants the prize – or if he’s just doing this to prove himself to someone unworthy of the proof.