How to Make It
Preheat oven to 300°F. Line a large rimmed baking sheet with parchment paper or a Silpat.
Place toasted almonds and hazelnuts in a food processor; pulse until coarsely ground. Set aside.
Place egg whites in bowl of a stand mixer fitted with the whisk attachment, and beat on medium-low speed until they start to foam, about 30 seconds. Gradually add granulated sugar, beating on medium-low speed until mixture forms stiff, glossy peaks, 8 to 10 minutes. Add salt, cinnamon, and vanilla extract, and beat until just combined.
Using a spatula, gently fold in half of the ground almonds and hazelnuts until combined. Repeat with remaining ground nuts.
Spoon meringue, a scant 1/3 cup at a time, onto prepared baking sheet. Bake in preheated oven until tops are golden, about 30 minutes, rotating pans halfway through baking.
Let meringues cool completely on baking sheet set on a wire cooling rack. When ready to serve, dust with powdered sugar, if desired.