Preheat oven to 350F and line a 9×9 baking pan¹ with parchment paper²
Combine butter and ½ cup (100g) semisweet chocolate chips in a large, microwave-safe bowl. 12 Tablespoons (170 g) unsalted butter, ½ cup (100 g) semisweet chocolate chips
Microwave for 30 seconds. Stir well, microwave for another 15 seconds and then stir well again. Repeat for 15 seconds until chocolate and butter are completely melted and well-combined.
Add cocoa powder and instant coffee (if using), stir well.½ cup (50 g) natural cocoa powder (unsweetened), ½ teaspoon instant coffee grounds
Add sugars, stir until completely combined.¾ cup (150 g) light brown sugar, ¾ cup (150 g) sugar
Add eggs, one at a time. After each addition, stir well, and then stir another 30 seconds (the better you stir your batter, the cracklier your brownie tops will be).2 large eggs + 1 large egg yolk
Stir in vanilla extract and salt.1 teaspoon vanilla extract, ½ teaspoon salt
Add flour, stir until completely combined. You cannot overmix this batter, make sure it is mixed very well.1 cup (125 g) all-purpose flour
Stir in chocolate chips.¾ cup (150 g) semisweet chocolate chips
Spread into prepared 9×9 pan.
Optional: for crackle-topped brownies: Place pan with batter in refrigerator for 15-30 minutes to chill (you can skip this step if you don't have the patience to wait!).
Remove from refrigerator and bake on 350F (177C) for 30-35 minutes or until a toothpick inserted in center comes out slightly fudgy, but not wet with batter.
Allow to cool before cutting and serving.