Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, combine the peanut butter, egg, erythritol, vanilla extract, baking soda, and salt. Mix until a smooth dough forms.

Scoop rounded tablespoons of dough and roll them into balls. Place the balls about 2 inches apart on the prepared baking sheet.

Using a fork, gently press down on each cookie dough ball to create a crisscross pattern. This will flatten them slightly and give them the classic peanut butter cookie look.

Bake for 10-12 minutes, or until the edges are lightly golden and the cookies are set. They will firm up more as they cool.

Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.