preheat the oven to 350.set the butter out to soften.spread the chopped pecans on a rimmed baking sheet and toast for about 4-6 minutes, until lightly browned and fragrant. let cool.put the softened butter in a large bowl. beat the butter, confectioners' sugar, vanilla bean seeds, vanilla extract and salt at medium speed until fluffy.add the flour, mixing in 1/2 at a time. beat at low speed until just incorporated. stir in the pecans and cacao nibs. mix well.transfer the dough to a work surface and roll into a 1 1/2-inch-thick log. wrap the log in plastic or parchment paper and refrigerate 1 hour, until chilled.line 2 large baking sheets with parchment paper. spread the vanilla sugar on a platter.mix the egg and water together to create an egg wash. brush the log with the egg wash and roll in the sugar. slice the log into 1/2-inch-thick rounds. place them on the prepared baking sheets, about 1 inch apart.bake the cookies for about 15 minutes, until the edges are golden; rotate the baking sheets from top to bottom and front to back halfway through baking. transfer the cookies to a wire rack and let stand until completely cooled.
