Adjust the oven racks to the upper-middle and lower-middle positions and preheat the oven to 375 degrees. Line 2 large baking sheets with parchment paper.
Place the 1/2 cup of granulated sugar in a shallow pie plate.
In a medium bowl, whisk the flour, cocoa powder, baking soda, and salt together. In a small bowl, whisk the corn syrup, egg white, and vanilla together.
In a large bowl, beat the butter, brown sugar, and remaining 1/3 cup granulated sugar with an electric mixer at medium speed until light and fluffy, 3 to 6 minutes. Beat in the corn syrup mixture until fully incorporated, about 20 seconds, scraping down the bowl and beaters as needed. Reduce the mixer speed to low and add the flour mixture and chopped chocolate; mix until just incorporated, about 30 seconds, scraping down the bowl and beaters as need. Give the dough a final stir with a rubber spatula to ensure that no pockets of flour remain at the bottom. Chill the dough for 30 minutes to firm slightly (do NOT chill longer than 30 minutes).
Divide the dough into 16 potions, each about 2 tablespoons, and roll the dough into balls. Working in batches, drop 8 dough balls into the pie plate with the sugar and toss to coat. Place the cookies on the prepared baking sheets, spacing them about 2 inches apart, 8 dough balls per sheet. (TIP: The dough can be portioned and shaped into balls and then frozen on a tray or large plate; when they are frozen solid, transfer them to a large zipper-lock bag. To bake, arrange the frozen cookies on the baking sheet - DO NOT THAW - and bake as directed, increasing the baking time to 16 to 21 minutes.).
Bake until the cookies are puffed and cracked and the edges have begun to set but the centers are still soft (the cookies will look raw between the cracks), 10 to 11 minutes, switching and rotating the sheets halfway through the baking time. DO NOT OVERBAKE!
Cool the cookies on the baking sheets for 5 minutes, then use a wide metal spatula to transfer the cookies to a wire rack; cool the cookies to room temperature before serving. (The cookies can be stored in an airtight container at room temperature for up to 3 days.).