Preheat your oven to 350°F. Line 3 baking sheets with parchment paper. Set aside.: The moment you preheat, the kitchen will start to warm and you may notice a faint scent of heated metal from the oven, which means it is approaching baking temperature. Preheating ensures the cookies begin baking immediately, creating lift and the recognizable crackled top. Lining with parchment paper prevents sticking and promotes even browning. A common mistake is skipping preheating which causes uneven spread and flatter cookies, so always wait until the oven reaches a steady 350°F before you slide the trays in.
In the bowl of your mixer add the softened butter and sugar and mix until well combined.: As you cream the butter and sugar , you will notice the mixture become paler and slightly fluffy, and you may hear the mixer change tone as air incorporates. This aeration is why the cookies have structure and tenderness. If the butter is too cold, it will not cream smooth, leading to lumps; if it is too warm, the mixture will be greasy and will not trap air. Aim for softened but not melted butter .
Add the eggs, one at a time and continue mixing until light and fluffy. Stir in the Grand Marnier.: When you add each egg , the batter will look glossy and slightly looser, and beating until light helps build a network that supports the cookie while keeping it tender. The addition of Grand Marnier introduces a warm citrus aroma that complements the cocoa powder . A frequent error is adding cold eggs which can cause the mixture to seize, so bring eggs to room temperature before using.
In another large bowl combine the flour, cocoa powder, baking powder and salt.: Sifting these dry elements together will create a uniform mixture and a fine dusting of cocoa powder that disperses evenly when folded in, preventing streaks. You will notice a rich, bittersweet cocoa scent when you mix them, which signals balanced chocolate flavor. If you skip sifting, lumps can remain and cause uneven texture in the baked cookies.
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.: As the dry mix incorporates, the dough will thicken and take on a dense, satiny appearance. Chilling solidifies the butter , making the dough easier to portion and promoting the thick, fudgy interior. The cold also slows spread so the crack pattern forms nicely. Over mixing at this stage activates gluten and yields tough cookies, so stop once the streaks disappear. If you are short on time, a minimum four hour chill works, but overnight deepens flavor more.
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.: Rolling the dough creates the visual contrast once baked, with the outer powdered layer cracking open to reveal the dark chocolate beneath. As you roll, you'll feel the cool, slightly tacky surface firm up from the chill, and pressing into the sugars leaves a matte, snowy finish. If balls are uneven, cookies will bake at different rates, so use a scoop for consistent results. If the dough sticks to your hands, chill it a bit longer.
Transfer the cookie 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.: When spaced correctly, each cookie has room to expand into a rounded, cracked dome while edges brown lightly. The visual cue to look for in the oven is a puffed, cracked surface. Crowding the sheet can result in merged cookies with flatter tops, so respect the spacing. If you do not have enough sheets, bake in batches and allow the sheet to return to room temperature between batches for more consistent results.
Place the baking sheets to the preheated 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.: During baking you will smell an intensified chocolate aroma and hear a faint sizzle as moisture evaporates. The cookies should look puffed with glossy cracks and slightly set edges while the centers remain soft. Rotating the sheets ensures even browning because ovens often have hot spots. Overbaking will dry them out, so remove them when edges are set but centers still look tender.
Let the cookies cool for 5 minutes on the baking sheets, then transfer them to racks to cool completely.: The first five minutes on the sheet allow the cookies to finish setting without breaking apart, and you may notice steam rising as they release residual heat. Transferring to a rack prevents the bottoms from becoming soggy and helps them firm to the perfect bite. A common misstep is moving them too soon, which can cause them to collapse, so give them that brief rest before lifting onto the rack.