1. Preheat oven to 375 degrees F and line muffin pan with foil liners. For cupcakes, mix the dry ingredients together. Mix the wet ingredients together and then add them to the dry ones. Add the chocolate chips.
2. Scoop batter with 1/4 measuring cup (make sure you get it from the bottom so that there are chocolate chips in it) and spoon it into prepared pan. Bake for 25 minutes.
3. To make peanut butter filling, mix everything together. When cupcakes are cool enough to handle, cut out big holes in the top of the cupcakes and fill with 1/2 heaping tablespoon peanut butter filling.
4. Spread out filling a bit and put the big chunk of cake back on and press it down a wee bit.
When they are done, the chocolate chips all sink to the bottom and they are so good. I like to wait a little while after I stuff them so that the peanut butter somewhat melts a bit and it is not just like a glob of peanut butter that was put inside, but more like it spontaneously generated there. Also, I would recommend eating when they are cool because the chocolate chips get hard again and it adds a happy crunchy texture. Enjoy!