Preheat the oven to 350 degrees, and line your baking pan** with parchment paper or non-stick tin foil. Set aside.
With a standing mixer or a hand mixer, cream the unsalted butter and peanut butter together, until light and fluffy.
Next, add in the brown sugar and the granulated sugar. Cream the mixture until well combined.
Next, add in the egg and mix until combined.
Add in the vanilla extract. Mix until combined.
Finally, add in the salt, baking soda, and all purpose flour. Mix until all ingredients are combined.
Press 2/3 of the peanut butter cookie dough into an even layer in the bottom of the prepared baking dish.
Next, spread the jam/jelly over the top of the cookie dough in an even layer (or as even as possible).
Next, if adding fresh berries, sprinkle them over the top of the jam.
Take the remaining peanut butter cookie dough and spread it over the top of the jam. Take a little dough at a time, flatten it into your hand, and then place it on top of the jam.
(It’s okay if not all of the jam is covered, but flattening the dough will help to cover more of the jam as well as help the cookies to bake more evenly.)
Sprinkle the top with peanuts.
Bake for 40-45 minutes, or until the tops of the cookie bars are golden brown and the center is set. If the bars are browning too quickly, tent a piece of non-stick foil over the top of the bars and continue cooking.
Allow to cool before cutting and serving.
Store leftovers in an airtight container at room temperature or in the fridge.