Start by preheating your oven to 375F. Get two baking sheets ready by lining them with parchment paper.
Mix dry ingredients. Sift together the flour, cocoa powder, baking soda, and salt into a bowl.
Cream the butter and sugars. In a large bowl, beat the softened butter with both sugars until light and fluffy, about 3 minutes.
Add the egg and vanilla. Continue beating until they're well incorporated, making sure to scrape the sides of the bowl.
Combine wet and dry. Gradually mix in the dry ingredients on low speed, just until blended. Then, fold in the chocolate chips.
Shape the cookies. Scoop the dough into 1½ tablespoon-sized balls and place them on the prepared sheets, spaced about 2 inches apart.
Bake for 10 minutes. Look for firm edges and a dry-looking center. After baking, let them cool on the sheets for 5 minutes before transferring to wire racks.