Preheat the oven to 350°F (175°C). Line 2 large baking sheets with parchment paper or silicone baking mats so the brookies don’t stick and spread evenly.
In a medium microwave-safe bowl, combine 1/2 cup of the semisweet chocolate chips and the unsalted butter. Microwave in 20–30 second bursts, stirring after each, until melted, smooth, and glossy. Let cool for about 5 minutes until warm but not hot.
1 cup semisweet chocolate chips, 4 tablespoons unsalted butter
In a large bowl, whisk together the granulated sugar, light brown sugar, and eggs for 1–2 minutes, until the mixture looks thicker, slightly paler, and a bit ribbony. This helps create shiny, crackly tops.
2/3 cup granulated sugar, 1/4 cup light brown sugar, 2 large eggs
Slowly pour the warm melted chocolate-butter mixture into the egg mixture while whisking constantly. Add the vanilla extract and whisk until smooth, thick, and glossy.
1 cup semisweet chocolate chips, 4 tablespoons unsalted butter, 2 large eggs, 2 teaspoons pure vanilla extract
In a separate bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, and fine sea salt, breaking up any lumps of cocoa.
3/4 cup all-purpose flour, 1/4 cup unsweetened cocoa powder, 1 teaspoon baking powder, 1/4 teaspoon baking soda, 1/2 teaspoon fine sea salt
Add the dry ingredient mixture to the chocolate mixture. Gently fold with a rubber spatula or wooden spoon just until no dry streaks remain. The batter will be thick and sticky, between brownie batter and cookie dough. Do not overmix.
3/4 cup all-purpose flour, 1/4 cup unsweetened cocoa powder, 1 teaspoon baking powder, 1/4 teaspoon baking soda, 1/2 teaspoon fine sea salt
Fold in the remaining 1/2 cup chocolate chips or chunks until evenly distributed throughout the batter.
1 cup semisweet chocolate chips, 1/2 cup chocolate chips or chunks
Let the batter rest at room temperature for 15–20 minutes to thicken and allow the flour to hydrate. The dough should become scoopable; if scooped too soon, the cookies may spread too much.
Using a medium cookie scoop (about 1 1/2 tablespoons), scoop mounds of dough onto the prepared baking sheets, spacing them about 2 inches apart. For extra-pretty tops, press a few additional chocolate chips into each mound.
Bake one sheet at a time for 9–11 minutes, until the tops are shiny, crackly, and just set around the edges. The centers should still look slightly soft and a bit puffed; they will continue to firm up as they cool.
Let the cookies cool on the baking sheets for at least 10 minutes before transferring to a wire rack to cool completely. Serve once set for the best chewy, fudgy texture.