Pre-heat oven to 350 degrees.
In a medium bowl, whisk together flour, baking powder and salt. Set aside.
In the bowl of a stand mixer, beat together butter, peanut butter, sugar and vanilla until light and fluffy, about 2 minutes.
Add in egg and beat to combine.
Add in flour mixture and stir on low just to combine.
Stir in chocolate chips.
Spread batter in to a 10" baking dish.
Bake just until sides are set and the pie is lightly browned and puffy. The middle will still be quite soft. (Trust the process!) This took around 10-14 minutes in a toaster oven and probably 18-20 in a big oven.
Cool for 10 minutes and then run a sharp knife around the edges.
Allow pie to completely cool, about 4 hours, before inverting on a serving plate or cutting to eat.