Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Sift together the unsweetened cocoa powder, baking soda, and salt in a separate bowl.
In a large mixing bowl, combine the creamy peanut butter, granulated erythritol, egg, and vanilla extract until smooth.
Gradually add the sifted dry ingredients into the wet mixture and stir gently until fully incorporated.
Scoop out the cookie dough onto the prepared baking sheet, spacing them about 2 inches apart, and flatten each cookie slightly.
Bake the cookies for 10-12 minutes, or until the edges are set and the tops look slightly cracked. Let them cool on the baking sheet for about 5 minutes before transferring to a wire rack.