How to Make It
Preheat oven to 350°. Line 2 large baking sheets with parchment paper.
Combine sugars and coffee granules in the bowl of a stand mixer. Melt butter in a medium saucepan over medium-high heat. Cook 3 to 4 minutes or until butter bubbles and begins to brown. Pour butter over sugar mixture; beat at medium-low speed for 2 minutes. Beat in vanilla and 3/4 teaspoon salt. Add eggs and egg yolk; beat until just combined.
Whisk together flour, cornstarch, baking powder, and baking soda in a medium bowl. Add flour mixture to sugar mixture; mix at low speed until just combined. Stir in chocolate. Refrigerate dough at least 1 hour.
Scoop half of dough into 16 equal balls (about 1 1/2 tablespoons each) and place 8 balls, about 2 inches apart, onto each prepared baking sheet. Bake 8 minutes. Rotate pans; bake 6 to 7 minutes or until edges are golden brown. Sprinkle cookies evenly with 1/4 teaspoon salt; let cool on baking sheets 5 minutes. Transfer to wire racks to cool completely. Repeat with remaining dough and remaining 1/4 teaspoon salt.