Combine 1 cup flour and the nuts in a food processor and process until finely ground. Add in 1/2 cup sugar, salt, cinnamon and remaining 1 cup flour and process until combined. Add butter and vanilla to food processor and pulse, in short bursts, until it comes together to form a dough.

Divide the dough into two pieces and then wrap each piece in plastic wrap or wax paper, rolling to shape into logs. Chill until firm, for at least 1 hour or overnight.

Preheat oven to 350°F. Line two baking sheets with parchment paper, and set aside.

Slice the logs into 1/4-inch rounds and place on the prepared baking sheets, about 1-inch apart. Bake until lightly golden around the edges, about 15 minutes, switching and rotating sheets halfway through baking. Cool for about 5 to 8 minutes.

Transfer remaining 1/4 cup sugar to a shallow bowl. Working quickly, spread about 1 to 2 teaspoons of Nutella on bottom of half of the warm cookies. Then press remaining cookies onto Nutella to form sandwiches. Roll cookies in sugar, while they're still warm, to coat. Cool completely on wire racks. Leftovers can be stored in an airtight container at room temperature for up to 4 days. Enjoy!