Preheat oven to 350° F and line 3 baking sheets with parchment paper. Set them aside for later.
Slice the cold butter into ¼ inch cubes and place them in the standing mixer, along with the brown and granulated sugars. Gradually increase speed and mix on high for 3-4 minutes until creamy. Scrape down the sides of the bowl with a rubber spatula halfway through.
1 cup unsalted butter, 1 cup light brown sugar, ¾ cup granulated sugar
In a separate bowl, whisk together the cocoa powder, flour, sea salt, cornstarch, baking soda, and baking powder. Set aside.
⅔ cup Dutch process cocoa powder*, 2 ¼ cup all purpose flour, 1 teaspoon fine sea salt, 2 teaspoon cornstarch, ¼ teaspoon baking soda, 1 teaspoon baking powder
After creaming the butter and sugar, add the eggs and vanilla extract to the standing mixer. Mix on medium speed until smooth and creamy. Scrape down the sides of the bowl halfway through.
2 large eggs, 1 tablespoon vanilla extract
Add mixed dry ingredients to the standing mixer and mix on the lowest setting until just combined. I like to let the dough sit for about 5 minutes for the flour to absorb some of the liquid, making the dough easier to work with.
Add the granulated sugar and powdered sugar to two separate small bowls.
½ cup granulated sugar, ½ cup powdered sugar
Roll the cookie dough into 12 balls. Roll each ball of cookie dough in the granulated sugar.
Then generously roll each ball of cookie dough in the powdered sugar***.
Add 4 balls of cookie dough to each baking sheet. Bake each baking sheet individually for about 12-14 minutes, or until cracking.
Immediately out of the oven, use a large, round cookie cutter to round out the edges of each cookie. (optional)
Let the cookies cool on the baking sheets completely before frosting.