Preheat oven to 350 degrees. Line a cookie sheet with parchment paper.
Sift together flour, cocoa powder, baking soda, and salt, then set aside.
In a large bowl, use a mixer, cream butter and white and brown sugar until well combined, for about 2 minutes.
Add eggs one at a time, mixing well after each addition, 1-2 minutes.
Add vanilla, beat until incorporated, 30 seconds.
Add flour mixture, mixing until just incorporated, 30-45 seconds.
Stir in chocolate chips.
Drop dough onto a cookie sheet in tablespoon-sized balls. Bake for 8 minutes, or until the edges of the cookies are set and the center is slightly soft. The recipe makes 50-60 cookies, depending on size.
Notes
Store cookies in an air-tight container at room temperature for up to 7 days.
Baked cookies can be stored in the freezer for up to 3 months. Wrap them in plastic wrap and store them in a freezer bag or container.
The dough is dark, so it can be hard to tell when the cookies are done. Use a timer for the recommended time of 8 minutes. Check the first batch for doneness, set around the edges with the center remaining soft. Adjust accordingly for the following batches.
Add 1 cup of semi-sweet chips to the dough for an extra bit of chocolate.