How to Make It
Preheat oven to 350°F. Stir together flour, cocoa, baking soda, and salt in a large bowl. Set aside.
Beat butter, brown sugar, and granulated sugar in bowl of a stand mixer fitted with a paddle attachment on medium-high speed, until fluffy, about 3 minutes. Add egg and vanilla, and beat on medium speed until well combined, about 1 minute. With mixer running on low speed, gradually add flour mixture, beating until just combined, about 1 minute. Fold in chopped chocolate and 3 tablespoons of the cacao nibs.
Transfer cookie dough to a large sheet of parchment paper. Cover top with another sheet of parchment and roll out dough into a 9-inch round, trimming edge as needed. Remove and discard top layer of parchment; transfer dough round on parchment paper to a large baking sheet. Sprinkle with sea salt and remaining 1 tablespoon cacao nibs, pressing lightly into dough to adhere.
Bake until just set around edges, about 15 minutes. Let cool on baking sheet 10 minutes, cut into wedges, and serve warm. Or let cool completely on baking sheet, about 20 minutes, before cutting into wedges.