Preheat oven to 350F and line 8x8 pan with parchment paper and nonstick spray.
In a large bowl, using a hand mixer, beat together butter, peanut butter, and brown sugar until smooth.
Mix in eggs and vanilla and once creamy, set aside.
In a medium sized bowl, whisk together flour, baking powder, and salt.
Slowly add dry ingredients to wet ingredients, using hand mixer, and mix until all incorporated.
Stir in peanut butter chips. Pour into greased baking dish and bake for 30-34 minutes or until toothpick inserted in middle comes out clean and just starting to turn golden brown on top.
Let cool completely. Once cooled, ice blondies with marshmallow fluff and drizzle on peanut butter.
Cut into 12 pieces. Enjoy!