Glittering Nutella Sandwich Cookies

Preheat the oven to 350 °F and line two large baking sheets with Silpats or parchment paper. In a medium bowl, whisk together the flour, cornstarch and salt. In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and confectioners’ sugar until it is light and fluffy then add the vanilla extract and continue beating. Add the flour mixture and beat just until combined and a soft dough forms. Place the various colors of sanding sugar into small bowls. Roll about 2 teaspoons of dough into a ball then place it in the sugar and roll it around so it’s thoroughly coated. If needed, lightly re-roll the ball so it’s evenly shaped then place it on the baking sheet. Repeat the rolling and coating process with the remaining dough, alternating sanding sugar colors and spacing the cookies 1 inch apart on the baking sheets. Bake the cookies until the tops are slightly cracked and the bottoms are pale golden, 12 to 15 minutes. Let the cookies cool on the baking sheets for 5 minutes then transfer them to a wire rack to cool completely. Once cooled, spread about 1 teaspoon of Nutella on the flat side of one cookie then sandwich it together with a second cookie. Repeat the filling and sandwiching process with the remaining cookies.