Hazelnut and Crème Fraîche Meringues with Lemon and Parmesan

Preheat oven to 350°F. Spread hazelnuts in an even layer on a rimmed baking sheet. Bake in pre- heated oven, stirring occasionally, until toasted and fragrant, 8 to 12 minutes. Let cool slightly, about 5 minutes. Wrap hazelnuts in a kitchen towel, and rub together to loosen skins. Let cool completely, about 10 minutes. Discard skins. Chop hazelnuts; set aside.

Reduce oven temperature to 175°F. Beat egg whites in a stand mixer fitted with the whisk attachment on medium speed until foamy, about 30 seconds. With mixer running on medium speed, gradually add sugar, 1 tablespoon at a time, beating until sugar is dissolved and mixture forms stiff, glossy peaks, 6 to 8 minutes.  

Line 2 baking sheets with parchment paper. Transfer meringue mixture to a large piping bag fitted with a 1-inch sultan raised cone tip (such as Ateco 796). Hold piping bag with the tip perpendicular to 1 prepared baking sheet about 1/2 inch above the surface; squeeze bag to pipe a 21/4-inch ring of meringue. Repeat process with remaining meringue mixture to form 32 rings, spacing rings at least 1 inch apart on prepared baking sheets. (Alternatively, use a 1-inch open star tip to pipe meringue into 21/4-inch rings.) Sprinkle meringues with 1/4 cup chopped toasted hazelnuts; reserve remaining chopped toasted hazelnuts for garnish. Bake meringues at 175°F until crisp and dry, 2 hours and 30 minutes to 3 hours. Let cool completely on baking sheets, about 30 minutes. (Alternatively, turn oven off, and leave meringues in sealed oven overnight [up to 12 hours] to dry completely.)  

While meringues bake and cool, line a baking sheet with parchment paper, and set aside. Stir together sugar and 1/4 cup water in a medium saucepan. Cook over medium, stirring often, until sugar is dissolved and mixture registers 230°F on an instant-read thermometer, 4 to 6 minutes. Add raw hazelnuts; cook, stirring constantly, until sugar turns grainy and white, 4 to 6 minutes. Continue cooking, stirring constantly, until sugar remelts and hazelnuts become glazed in a dark brown syrup, 5 to 10 minutes. Pour hot mixture onto prepared baking sheet, and spread in a single layer. Sprinkle with fleur de sel. Let cool completely, about 30 minutes. 

Break hazelnut praline into pieces, and transfer to a high-powered blender. Add 3/4 cup water; process until mixture forms a smooth, thick, and just pourable paste, 2 to 4 minutes, adding remaining 1/4 cup water, 1 teaspoon at a time, if needed to thin paste. Transfer mixture to a medium bowl. Set aside at room temperature until ready to use. 

Whisk together yogurt, sugar, and fleur de sel in a small bowl. Whisk crème fraîche in a separate small bowl until stiff peaks form, about 1 minute. Gently fold crème fraîche into yogurt mixture. Cover and refrigerate until ready to assemble, up to 12 hours.  

To assemble, turn half of meringues flat side up. Transfer crème fraîche mixture to a piping bag with a 1/2-inch hole snipped in the corner. Pipe about 1 1/2 teaspoons crème fraîche mixture in a circle on flat side of each meringue. Top with remaining meringues, flat side down. Pipe about 1 1/2 teaspoons crème fraîche mixture into top hole of each assembled meringue sandwich. Drizzle about 1 1/2 teaspoons hazelnut praline over center of each meringue sandwich, allowing to drip down the sides. Reserve remaining hazelnut praline for another use, or serve alongside meringues. Garnish with lemon zest, Parmesan cheese, and reserved chopped toasted hazelnuts. Serve immediately.