Preheat the oven to 350 and line a cookie baking sheet with parchment paper. Lightly spray the parchment paper with cooking spray.
In a large mixing bowl, whisk together melted butter and brown sugar until combined.
Whisk in the egg.
Whisk in vanilla and peanut butter.
Sift in flour, baking soda and salt. Mix until just combined. You will need to use your hands here and work the cookie dough until flour is no longer visible.
Fold in peanut butter morsels, mini chocolate chips and white chocolate chips until evenly distributed.
Form one inch balls with the cookie dough and place then on the baking sheet about 2 inches apart.
Using a greased fork, make criss-cross indentations while lightly flattening the cookie dough. You may have to shape the sides of some cookies back.
Bake for 8-9 minutes.
Cool these yummy...crispy on the outside and gooey, chewy on the inside cookies on a cooling rack to room temperature!