Preheat an oven to 350°F. Bring a small pot of water to a boil over high heat and add the hazelnuts. Boil for 30 seconds, then drain. Immediately wrap the hot hazelnuts in a dishtowel and rub them in the folds of the towel to remove the brown skin. Some bits of skin may cling to the nuts, but remove as much as you can. Put the skinned hazelnuts on a baking sheet and bake until golden brown and fragrant, 5 to 8 minutes. Let cool, then chop very coarsely.
Set aside 2/3 cup blueberries. Put the remaining blueberries in a saucepan with 2 tablespoons plus 2 teaspoons maple syrup. Cover and cook over medium-low heat, stirring occasionally, until the berries collapse completely and release their dark purple juice, about 5 minutes. Remove from the heat and stir in the reserved blueberries. The mixture will be thin. Transfer to a small bowl, cover, and chill.
At serving time, divide the yogurt among 4 parfait glasses or wine glasses. Top each portion with some of the chilled blueberries and hazelnuts, dividing them evenly, and with 1 teaspoon maple syrup. Serve immediately.
Note: To make drained yogurt, scoop yogurt into a sieve or colander lined with a triple thickness of dampened cheesecloth. Set over a bowl to collect the whey. Cover with a plate or cloth to protect the yogurt (you’re not pressing it) and refrigerate until it has the consistency of Greek yogurt, 1 to 2 hours.
Servings 4