Add all the ingredients except for the chocolate chips to a bowl and mix until well combined and smooth (using an electric hand mixer or just by hand).
Fold in the chocolate chips.
Pour the batter into a small 6-inch cake pan (or a 9x5 bread pan).
Bake at 350 for 30 minutes or until a toothpick comes out mostly clean.
To Make Frosting
Add the peanut butter and chocolate chips to a bowl and melt using the double boiler method or in intervals in the microwave.
Once smooth, drizzle or spread on top of the cake.
Video
Notes
I made this using a small 6-inch cake pan. I think doubling the recipe might work but I haven't tried it so I can't say for sure.