Whisk flour, salt, and activated charcoal in a bowl and set aside.
Using a standing or handheld mixer, cream the softened butter and sugar on medium until fully mixed together, about 45-60 seconds.
Scrape down the sides of the bowl and add the egg and vanilla.
Mix on low, increasing to medium until fully combined, about 30-60 seconds.
Add the flour mixture. Starting on low, mix for about 30 seconds. Slowly increase speed to medium. Once the dough starts to clump in the middle it’s done. You should be able to press your finger into the dough and it will indent and not stick.
Divide your dough in half. If you’re saving you dough to bake at a later time, form two disks and wrap tightly in plastic. Store in an airtight container or ziploc bag in the fridge or freeze until ready to bake.
Otherwise, roll out each slab of dough to ¼ - ½ inch thick on floured parchment. Be sure to add a little bit of activated charcoal to the flour when rolling it out.
Cover with another piece of parchment and stack on a baking tray.
Chill in the fridge 1 hour.
At this time, preheat your oven to 350 degrees.
After the dough has chilled, remove from the fridge and cut out the cookies. Re-roll the scraps of dough, and re-chill the dough until firm.
Place the cut out sugar cookies on a parchment or silicone mat lined baking sheet.
Optional: Rechill the cut-out cookies for 10-15 minutes in the fridge or freezer to further prevent spreading.
Depending on size, bake for 8-12 minutes.
Let cool 5 minutes on baking pan, then remove to a wire rack to finish cooling.
Let cool completely before frosting.