Mix the maple syrup and vanilla, then brush all over the nectarines. Sprinkle the cut sides with the brown sugar.
Place the nectarines, cut side down, on the grill and cook until charred, then flip and cook the other side.
Serve over ice cream, drizzled with a little maple syrup and sprinkled with hazelnuts.
Notes
When grilling fruit directly on the grill, make sure the heat isn’t too high as the sugars in the fruit can easily caramelize and burn quickly. When choosing a nectarine, buy ones that give in to pressure but just slightly. An underripe nectarine will not become sweet and an overripe one will have a mushy texture. If you don’t want to put the nectarines right on the grill, brush them with maple syrup, sugar, and vanilla, then add them to a sealed foil packet and leave on the grill for 15-20 minutes agitating them halfway through for even cooking.