In the bowl of a stand mixer fitted with a paddle attachment, cream the room temperature butter, peanut butter and sugars together until light and fluffy, approximately 5 minutes on medium speed.
Scrape down the bowl with a rubber spatula half way through mixing.
Add the eggs, beating well after each addition. Stir in the vanilla extract.
Whisk together the flour, baking soda and salt.
Gently mix the dry ingredients into the butter mixture. Fold in the chocolate chips.
Line a 9x13inch / 33x23cm baking pan or dish with parchment paper.
Press the dough into the bottom of the prepared pan then sprinkle over peanuts and extra chocolate chips (optional).
Place in the oven and allow to bake for 15-20 minutes until golden brown and a skewer inserted comes out clean.
Remove from the oven and allow to cool for 30 minutes on a wire rack before slicing the peanut butter bars and serving.