Heat the butter, chocolate and 1 3/4 cups granulated sugar in a medium saucepan over low heat, stirring, until melted and smooth. Let cool slightly, then add the Grand Marnier and eggs and stir until combined. Add the flour mixture and stir until just combined. Transfer to a bowl, cover and refrigerate until firm, about 2 hours.
Position racks in the upper and lower thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper. Put the remaining 1/4 cup granulated sugar and the confectioners' sugar in 2 separate shallow bowls. Form the dough into 1-inch balls. Add the dough balls, a few at a time, to the granulated sugar and roll to coat, then transfer to the confectioners' sugar and roll to coat. Arrange about 1 1/2 inches apart on the prepared baking sheets.
Bake, switching the pans halfway through, until the cookies are puffed and cracked, about 12 minutes. Let cool 5 minutes on the baking sheets, then transfer to racks to cool completely.