How to Make It
In a food processor, pulse the hazelnuts and cocoa nibs until coarsely ground. Scrape into a medium bowl and whisk in the flour, cocoa powder, salt and cinnamon.
In the bowl of a stand mixer fitted with the paddle, beat the butter with the confectioners’ sugar and vanilla bean paste at medium speed until light and fluffy, about 3 minutes. Add the dry ingredients and beat at low speed just until incorporated. Scrape the dough onto a work surface and form into a ball. Halve the dough, then shape each half into a 1 1/2 -inch square log and wrap in parchment paper. Freeze until firm, at least 2 hours or overnight.
Preheat the oven to 350°. Line 2 large rimmed baking sheets with parchment paper. Working in 2 batches, cut the cookie-dough logs into 1/4-inch-thick slices and arrange on the prepared sheets at least 1 inch apart. Bake the cookies for about 15 minutes, until lightly browned on the bottom; rotate the baking sheets from top to bottom and front to back halfway through baking. Let the cookies cool on the baking sheets for 5 minutes, then transfer to a rack to cool completely.
In a medium saucepan, bring 1 inch of water to a simmer. Place the milk chocolate in a heatproof small bowl and set it over the saucepan. Stir the chocolate until melted and smooth. Remove the saucepan from the heat; leave the bowl of chocolate on top. Dip 1 corner of each cookie in the chocolate to coat halfway, letting the excess chocolate drip back into the bowl. Transfer the cookies to parchment paper-lined baking sheets and refrigerate until the chocolate is set, about 20 minutes.