Whisk the flour, cocoa powder, baking soda, and salt together in a medium bowl and set aside.

In a stand mixer, combine the butter, brown sugar, and ⅓ cup granulated sugar together on medium-high speed until smooth and creamy, about 2 minutes Add the egg, vanilla extract, and chocolate extract and beat on high speed until combined, about 1 minute more. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine. Pour the dry ingredients into the wet ingredients, add the milk, and mix on low until combined. The cookie dough will be thick.

Roll balls of dough, approx 1 tablespoon each, and roll each into remaining ⅓ cup granulated sugar. Place cookie dough balls onto a large lined baking sheet. Using your thumb, make an indent into each cookie. Chill the shaped cookies for at least 2 hours in the refrigerator or 1 hour in the freezer

Preheat the oven to 350°F. Line a baking sheet with parchment paper or a silicone baking mat. Remove chilled and shaped cookies from the refrigerator. Divide between both baking sheets, spacing the cookies about 2-3 inches apart. Bake for 12-14 minutes or until the edges are set. Remove from the oven. The indents will have lost some shape or have puffed up, so use the end of a spatula to make an indent again into the warm cookies. Allow cookies to cool for 5 minutes before transferring to a wire rack to cool completely before filling with ganache