Preheat your oven to 350°F (175°C) and grease or line your baking dish with parchment paper for easy removal.
In a large mixing bowl, combine the room temperature butter and granulated sugar. Use your electric mixer to beat until light and fluffy, about 2-3 minutes.
Add the eggs and vanilla extract to the butter mixture. Beat until combined, ensuring everything is well-incorporated.
Next, add the creamy peanut butter to the mixture. Beat until the peanut butter is fully integrated and the mixture is smooth.
In a separate bowl, whisk together the all-purpose flour and baking powder. Gradually add this to the wet mixture, mixing on low speed until just combined.
Spread about two-thirds of the peanut butter batter into the prepared baking dish, smoothing it into an even layer.
Spoon your favorite jam over the batter, spreading it gently to cover as much as possible without disturbing the base layer.
Dollop the remaining peanut butter batter over the jam layer. Use a spatula to spread it out gently, ensuring some of the jam is still visible.
If using, sprinkle the coarsely chopped salted peanuts on top of the batter for added texture and crunch.
Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.
Let the bars cool in the pan for at least 10 minutes, then transfer to a wire rack to cool completely. Dust with powdered sugar before slicing into squares.
