Preheat oven to 325 degrees. 

In a large bowl, or stand mixer, combine flour, peanut butter powder, sugars, baking powder and salt. Stir to make sure that all ingredients are blended well, especially making sure that the peanut butter powder is evenly distributed. 

Next, add milk slowly, blending thoroughly. The first two times I made this, I just used plain milk. The third time, I used a milk to which i added vinegar. I'm not sure I could tell a big difference, but it definitely didn't' hurt. If you're going to add the vinegar to the milk, allow the milk to set for 5 minutes before adding to the batter. 

Finally, add peanut butter. Make sure to stir thoroughly, but don't over mix. If adding chocolate chips, do so after stirring in the peanut butter.

Pour into a greased or parchment paper lined loaf pan. (I've done it both ways.) I used a medium loaf pan, which helps with creating a taller loaf. It measures 8.5 x 4.5. You can use a large 9 x 5 loaf pan. Your loaf will just be shorter. 

Place in a 325 degree heated oven and bake for 50 minutes. The first time, I baked this at 350 for 40 minutes. However, it split along the top. (Although it was completely cooked in the center.)  The original recipe called for baking it at 325 for one hour.I think 50 minutes is more accurate. To prevent the top from over browning, you may want to cover with foil after the first 30 minutes. 

Remove from the oven and allow to cool in pan for about 10-15 minutes. This allows the sides to cool and firm up. Then remove from the pan and place on the rack to cool completely before slicing. Probably at least an hour.