Preheat your oven to 350 F degrees. Line 3 baking sheets with parchment paper. Set aside.
In the bowl of your mixer add the softened butter and sugar and mix until well combined.
Add the eggs, one at a time and continue mixing until light and fluffy. Stir in the Grant Marnier.
In another large bowl combine the flour, cocoa powder, baking powder and salt.
Gradually add the flour mixture to the mixer bowl and mix until combined. Do not over mix. Cover the bowl with plastic wrap and chill for 4 hours to overnight.
Place the remaining sugar and powdered sugar in 2 separate shallow plates or bowls. Form the dough into 1-inch balls. Use a cookie scoop for evenly sized cookies. Roll the cookie balls first in the granulated sugar and then in powdered sugar. Make sure they are coated properly.
Transfer the cookies balls to the prepared baking sheets and arrange about 1 1/2 inches apart. You should be able to fit about 12 cookies per sheet.
Place the baking sheets to the preheat oven and bake for 10 to 12 minutes until the cookies are puffed and cracked. If placing 2 cookie sheets at once, switch them halfway through.
Let the cookies cool for 5 minutes on the baking sheets, then transfer them to racks to cool completely.