Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine peanut butter, sugar, egg, and vanilla extract. Mix until smooth.
In another bowl, whisk together flour, baking soda, and salt. Gradually add to the peanut butter mixture, mixing until combined.
Roll dough into 1-inch balls and place on the prepared baking sheet. Flatten each ball slightly with a fork.
Bake for 10 minutes or until edges are golden. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
In a microwave-safe bowl, melt chocolate chips and vegetable oil in 30-second intervals, stirring after each, until smooth.
Dip half of each cooled cookie into the melted chocolate, allowing excess to drip off. Place on parchment paper to set.