Preheat oven to 350F and grease or line an 8x8 baking pan with parchment paper
Melt the butter and chocolate chips together in the microwave or double boiler. Mix in the creamy peanut butter and vanilla extract.
In a separate bowl combine the eggs and sugar and mix with an electric mixer or whisk attachment for a stand mixer until light and fluffy - about 3 minutes.
Gently fold the melted chocolate mixture into the eggs and sugar with a flat spatula. Fold in the cocoa powder and salt.
Pour the batter into the lined pan and smooth into an even layer. Optional: Drizzle extra peanut butter over the top and mix with a toothpick to make a swirl effect.
Place in the oven and bake at 350F for 28 minutes.
Cool completely and then cut into squares
Notes
I like to use creamy salted peanut butter for this recipe. if you use unsalted peanut butter, add an extra 1/4 tsp of salt.
You can use cashew butter or almond butter in place of the peanut butter
You can use 2oz of a semi sweet baking chocolate bar in place of the chocolate chips