Melt the butter in a skillet over medium heat. Add the onion and ginger and cook until tender, about 3 to 4 minutes. Add the nectarine and cook 1 to 2 minutes more. Add the brown sugar, balsamic and spices and cook, stirring occasionally, until the mixture begins to thicken slightly. Remove from the heat; cool to room temperature. Store in the fridge until ready to use.
Preheat the oven to 400 degrees F. Place the half baguette slices on a baking sheet; bake until lightly toasted, about 5 minutes. Cool until safe enough to handle, and then top each with a thin slice of brie. Top
the brie with a small spoon of the chutney and, if desired, a small herb sprig, such as parsley or rosemary.