Position a rack in the center of the oven and heat the oven to 350ºF. Line three large cookie sheets with parchment paper.

In a medium mixing bowl, whisk together the flour, baking soda, and salt. In the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl with a hand mixer), beat the butter, brown sugar, cocoa, orange zest, and vanilla on medium speed until well combined, for about 4 minutes. Add the eggs one at a time, beating briefly between additions. Add the cooled chocolate and mix until blended, about 1 minute. Add the dry ingredients and mix on low speed until almost completely blended, about 1 minute. Add the chopped chocolate and mix by hand until well incorporated.

Shape the dough into 1-1/4-inch balls with a small ice-cream scoop or two tablespoons. A 1.5-tablespoon capacity cookie scoop works well here.

Pour the granulated sugar into a shallow dish. Dip the top of each ball in the sugar and set the balls sugar side up about 1-1/2 inches apart on the prepared cookie sheets. Bake one sheet at a time until the cookies are puffed and cracked on top, 11 to 12 minutes. Let the cookies cool on the sheet for 5 minutes before transferring them to a rack to cool completely.