I deviated from the original recipe by adding the gruyere cheese to the topping. I thought the cheese gave added flavor to the dish. Next time, though, I'm going to prepare the dish without the cheese and see how it tastes. The maple syrup flavor is a wonderful foil for the bitterness of the brussels sprouts. The flavor of the maple syrup (and the pecans) might be stronger without competition from the cheese.
The photo posted with this recipe is a photo of the gratin before it is baked.