Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper for easy removal.

1. In a saucepan, melt the butter and chopped chocolate over medium heat, stirring occasionally until smooth. Once melted, remove from heat and allow to cool slightly.
2. In a separate bowl, whisk together the sugar, salt, eggs, and vanilla extract until well combined.
3. Slowly pour the melted chocolate mixture into the egg mixture and stir to combine.
4. Pour the batter into the prepared cake pan and spread evenly. Bake for 20-25 minutes or until a toothpick inserted in the center comes out with just a few moist crumbs. The cake should still be slightly soft in the center.
5. While the cake is baking, prepare the peanut butter layer. In a small bowl, mix the peanut butter and powdered sugar until smooth and creamy.
6. Once the cake has cooled completely, spread the peanut butter mixture evenly over the top of the cake.
7. For an extra touch, you can drizzle melted chocolate over the peanut butter layer or add chopped peanuts for crunch.
8. Chill the cake in the refrigerator for at least 2 hours to allow it to set before serving.
9. Slice and serve chilled or at room temperature.