Preheat the oven to 350F degrees. Line a 9x5 inch loaf pan with parchment paper along the long sides so that there's an overhang, then grease the exposed sides.
In a large bowl, whisk together the flour, baking powder and salt. Set aside.
In a separate bowl, beat together the peanut butter and brown sugar until there are no lumps of sugar (there will be granules - that's ok).
Beat the egg and vanilla extract into the peanut butter mixture.
Whisk the milk and sour cream into the peanut butter mixture. You can also do this with the mixer on a low speed.
Make a well in the middle of the dry ingredients and pour the peanut butter mixture into the middle of the dry ingredients. Gently fold the mixture together using a rubber spatula. If there are lumps of flour, whisk gently by hand. Do not use an electric mixer, as it can make the loaf tough.
Fold in the chocolate chips.
Pour or spoon the batter into your prepared loaf pan. It should only be about 2/3 to 3/4 full. If your pan is smaller, you will have excess batter which can be used to make a few muffins (bake for 15-20 minutes in the preheated oven).
Bake for 50-60 minutes in the middle of the preheated oven. When the loaf is ready, an inserted toothpick should come out clean or with a crumbs but no gooey batter. Check the loaf around 45 minutes, and if the top is getting too browned tent a piece of aluminium foil over the top of the pan. Once finished cooking, allow the loaf to cool completely before cutting in.