Preheat oven to 350.
Line an 8×8 pan with foil and lightly spray with non-stick spray. Set aside.
In a medium bowl, add the melted & cooled butter.
Stir the peanut butter into the butter until creamy and smooth.
Add the brown sugar to the butter/peanut butter and stir until smooth.
Add the egg and vanilla and stir to combine.
Add the flour, baking powder and salt to the peanut butter mixture and stir just to combine.
Gently fold in chocolate chips and peanut butter chips.
Pour into prepared pan spread evenly with a spatula. I like to tuck in a few more chocolate chips and peanut butter chips.
Bake for 20-30 minutes or until set in the middle.
Cool and then slice.