I think we need more context here to answer your question but I have two guesses. My first and best guess is that it refers to the autumn breeze. A breeze is always considered cold so the smell of caramel would be literally on the edges of the breeze. Meaning the author wants you to sense the cold air while reading this sentence but also to sense a faint smell of caramel in the air. “At the edges” means it’s not an overpowering smell. My second guess is that there is a sentence or paragraph before the sentence you are asking about that “at the edges of the cold” refers to.