Combine butter, sugar, salt, bourbon (if using), and vanilla extract in the bowl of a standing electric mixer. Beat on high speed until smooth and creamy but not fluffy, about one minute. On low speed, stir in pecans, cocoa nibs, and chocolate. Add flour and mix on low speed until the flour is incorporated.

Divide the dough in half. Working with one piece at a time, roll the dough into 12-inch logs about 2 inches thick. Wrap the dough logs in parchment paper and refrigerate for several hours or overnight, until the dough is firm and sliceable (dough can be frozen at this point for up to three months).

Using a sharp knife, cut the cold dough log into slices about 1/4-inch thick. Place cookies at least 1 1/2 inches apart on parchment lined baking sheets. Bake in an oven preheated to 350° F until the cookies are pale golden brown at the edge, about 12 to 14 minutes, rotating the baking sheets from top to bottom halfway through baking. Cool completely.