Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In a food processor, pulse the hazelnuts until they form a coarse meal; the pieces should not be larger than about 1/8 inch in diameter. Transfer the ground nuts to a bowl. Add the sugar, syrup, egg whites and zest. Using a rubber spatula, mix the ingredients together until well combined. Cover the dough with plastic wrap and let sit until slightly dry to the touch, about 10 minutes.
Using your hands or a small scoop, form or roll the dough into 1-ounce balls. Coat in maple sugar and top with a whole hazelnut by pressing it into the dough. Place on the prepared baking sheet and bake for 12 minutes. Let cool completely.