Preheat oven to 350 degrees Line baking sheets with either parchment paper or silicon baking mats.

Cream together brown sugar and softened butter. Add egg and vanilla and mix until combined.

In a separate mixing bowl, combine cocoa powder, flour, baking soda, and salt. Slowly add the powdered mixture to the wet ingredients until fully combined. Fold in peanut butter chips.

Loosely mold the batter into 1-inch balls and place about 2 inches apart on the cookie sheets (the dough does spread). Bake for about 10-12 minutes per batch.