Preheat the oven to 350 degrees and line a baking sheet with a silicone mat or parchment paper.
In a medium-size bowl, beat together the butter, peanut butter, and brown sugar with an electric mixer on medium speed. Beat until thoroughly blended and lightly fluffy, about 40 seconds.
Next, add the egg and vanilla and beat until combined.
Sprinkle the flour, baking powder, baking soda, and salt evenly over the the dough. Beat until just combined.
Finally, stir in the chocolate chips.
Press the dough flat in the bowl and roughly divide it in quarters by eye (you can also lightly score it with a knife). Make three dough balls out of each quarter of dough (making a total of 12 cookies).
Roll the dough balls lightly in your hands and then place them on the baking sheet, evenly spaced.
Bake for about 11 minutes. The edges will start to brown, but the centers will still appear soft. Let the cookies cool on the baking sheet for 1 minute before moving them to a wire rack to cool completely.