Preheat over to 350 deg F. Line a baking sheet with parchement.
Combine peanut butter, erythritol, egg, and vanilla in a bowl; mix well until a dough is formed.
Roll dough into 1 inch balls. Place on prepared baking sheet, and press down with a fork.
Bake at 350 until edges are golden, 12 - 15 minutes. Cool on the backing sheet for a minute, then remove to a wire rack and let cool completely.