Instructions

1. Place 1 stick unsalted butter in the bowl a stand mixer (or large bowl if using an electric hand mixer). Place 1 large egg on the counter. Let both sit at room temperature until the butter is softened, at least 30 minutes.
2. Place 1 cup all-purpose flour, 1/2 cup unsweetened cocoa powder, and 1 teaspoon baking soda in a medium bowl and whisk to combine.
3. Add 1/2 cup packed light brown sugar, 1/2 cup granulated sugar, and 1/2 teaspoon kosher salt to the bowl of butter. Beat on medium speed with the paddle attachment until fluffy, 3 to 4 minutes. Stop the mixer and scrape down the paddle and sides of the bowl. Add the egg and 2 teaspoons vanilla extract, and beat on medium speed until just combined.
4. Add the flour mixture and fold by hand with a flexible spatula or wooden spoon until just combined. Add 1 cup semisweet chocolate chips and fold until just combined. Cover the bowl and refrigerate for at least 3 hours or up to overnight.
5. Arrange 2 racks to divide the oven into thirds and heat the oven to 350ºF. Line 2 rimmed baking sheets with parchment paper. Scoop the dough in 2-tablespoon portions onto the baking sheets, spacing them evenly apart, 11 to 12 per sheet.
6. Bake until the cookies are set along the edges, 10 to 12 minutes. Let cool on the baking sheets for 5 minutes, then transfer to a wire rack and let cool completely.