In a medium microwave-safe mixing bowl, combine the chocolate and butter. Microwave on high in 20-second intervals, stirring between each, until the chocolate and butter are melted, about 2 minutes.
In a large mixing bowl, beat the sugars and eggs on medium speed until light and frothy. Add the melted chocolate mixture and vanilla and beat until combined. Add flour, cocoa powder, salt, and baking soda. Stir together with a spatula until mostly combined. Stir in chocolate chips and mix until the batter is well combined. Cover the bowl and chill the batter for 30 minutes.
Preheat the oven to 350°F Line two baking sheets with parchment paper.
Scoop the chilled dough into 2-tablespoon-sized balls and place on the prepared pans about 3 inches apart.
Bake for 8 to 10 minutes or until the cookies have spread and are shiny and cracked. (They will still be soft when hot and firm up as they cool.) Let cool completely on the pans.
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Notes
Use a hand mixer or stand mixer. The eggs need to be beaten for a long time (about 4 minutes) so enough air is incorporated to get perfectly crinkly brownie-esque tops. You can use a hand mixer or stand mixer fitted with the whisk attachment, then switch to the paddle when incorporating the flour. Keep in mind mixing by hand will not give you that same crackling effect, but will still produce a great cookie.
Use room temperature eggs. Cold eggs will not whip up nice and frothy, which will affect how your batter turns out.
Weigh the flour. Since fudgy, gooey cookies are the name of the game here, you don’t need much flour. Using too much flour will give you a dry cookie, which is the exact opposite of what you want! Use a kitchen scale for the most accurate flour measurement. If you don’t have one, fluff up your flour in its container before spooning it into a measuring cup and leveling it off with a knife.
Chill the cookie batter. If you skip this step, the cookies won't bake up properly and will turn out too thin and possibly burn on the edges. This is a very easy recipe that creates really delicious chocolate cookies, but time is an important ingredient!
Add espresso powder. If you want a more intense chocolate flavor, add ½ teaspoon instant espresso powder along with the cocoa powder and flour. The cookies won’t taste like coffee, I promise!
Use a scoop to measure the cookie dough. I scooped the dough in a very heaping ball using a #40 scoop. Bigger dough balls turned out the best in my tests for this brownie cookie recipe.