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

In a large mixing bowl, stir together the peanut butter, brown sugar, egg, and vanilla extract until the mixture is smooth and well combined.

Using a 2-inch cookie scoop, portion the dough and roll it into balls. Place these cookie balls on the prepared baking sheet, ensuring they have space to spread.

Flatten each ball slightly with a fork to create a criss-cross pattern.

Bake the cookies for 9 to 11 minutes, or until the edges are set and the tops look dry.

Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.