Make cookies: Preheat oven to 325°. Bake hazelnuts on a rimmed baking sheet until deep golden throughout, 12 to 16 minutes. Rub in a kitchen towel to remove loose skins. Let nuts cool, but don’t turn off oven.
In a food processor, whirl nuts and powdered sugar until finely ground. Beat egg white in a medium bowl with a mixer until frothy; then stir in nut mixture, salt, and vanilla until evenly moistened.
Drop mixture by 1-tbsp portions onto 2 rimmed baking sheets lined with parchment paper. Bake, swapping pan positions halfway through, until cookies are golden, about 12 minutes (for soft centers; for crisp centers, turn off oven after baking, and let cookies stand in oven about 20 minutes). Let cool on pans a few minutes, then transfer to racks to cool completely.
Assemble desserts: Combine yogurt and granulated sugar; spoon into 8 wide-mouth half-pint canning jars. Just before serving, spoon pluots on top, drizzle with honey if you like, and coarsely crumble 12 of the cookies over fruit.
MAKE AHEAD The cookies, up to 2 days, stored airtight. Up to 4 hours, chill the sweetened yogurt and fruit separately; assemble with cookies at serving time.