Preheat oven to 350 degrees. In a mixing bowl whisk together flour, baking soda and salt, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment, whip together 1/2 cup butter, 1/2 cup peanut butter, granulated sugar and brown sugar until pale and fluffy.
Mix in egg and vanilla. With mixer set on low speed, slowly add in dry ingredients and mix just until combined.
Shape dough into 2 Tbsp balls and drop onto Silpat or parchment paper lined baking sheets spacing cookies about 2 1/2 inches apart (dough will be sticky so if you don't want to roll it you can just drop onto baking sheets without rolling).
Flatten slightly and bake in preheated oven 10 - 12 minutes (you don't want cookies to be really soft or they will break when you try to coat them, they soften a bit more with the chocolate coating), remove from oven and allow to cool several minutes on baking sheet then transfer to a wire rack to cool completely.
Place powdered sugar in a shallow dish. In a medium microwave safe bowl, heat both kinds of chocolate chips, 1/4 cup butter and 1/4 cup peanut butter on HIGH power 1 to 1 1/2 minutes.
Remove from microwave, add in vanilla then stir mixture until smooth. Spread a thin layer of the chocolate coating over top of one cookie then dip into powdered sugar (without coating the bottom in powdered sugar or the chocolate coating wont stick well when added to bottom).
Then turn cookie to bottom side and spread a thin layer of chocolate coating over bottom and return to powdered sugar to coat. Repeat process with remaining cookies. Store in an airtight container at room temperature.