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

1. In a large mixing bowl, combine the peanut butter, sugar, egg, vanilla extract, baking soda, and salt. Stir until well combined. The dough should be thick and slightly sticky.
2. Scoop tablespoon-sized portions of dough and roll them into balls. Place the dough balls onto the prepared baking sheet, spacing them about 2 inches apart.
3. Flatten each dough ball with the back of a fork in a crisscross pattern.
4. Bake the cookies in the preheated oven for 10-12 minutes, or until the edges are golden brown. The cookies will firm up as they cool.
5. Remove the cookies from the oven and allow them to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
6. Once the cookies have cooled, melt the chocolate in a heatproof bowl over a pot of simmering water (double boiler method) or in the microwave, stirring every 20 seconds until smooth. If desired, add the vegetable oil to make the chocolate smoother and easier to dip.
7. Dip the bottom half of each cookie into the melted chocolate, allowing any excess chocolate to drip off.
8. Place the dipped cookies on a parchment-lined baking sheet and let them set until the chocolate hardens (this can take about 30 minutes, or you can speed up the process by refrigerating them).