Preheat oven to 350 degrees. Spray a 10 inch bundt pan with non-stick cooking spray. Dust the bundt pan with 2 T. cocoa powder. Tap out any excess cocoa powder. This will help keep the cake from sticking. Set aside.
In a medium microwave-safe bowl, add in the cubed butter and hot water. Place into the microwave for 2 and half minutes until the water is bubbling and the butter is melted.
Add in the vegetable oil, cocoa powder, and 1 cup of peanut butter. Whisk until everything is incorporated and smooth.
Add the sour cream and vanilla bean paste and whisk until combined and smooth.
In a separate bowl, add in the flour, sugar, baking soda, baking powder, and xanthan gum. Whisk until combined.
Pour the wet mixture into the dry ingredients. Add in the lightly beaten eggs. Stir with a spatula until all of the dry ingredients are incorporated. Switch to a whisk and whisk until the batter is smooth. I added in the eggs at this point to avoid cooking the eggs in the boiling water.
Pour the batter into the prepared bundt pan. Add in the remaining ¾ cup of smooth peanut butter in dollops on top of the batter. Using a butter knife or skewer, swirl the peanut butter into the batter.
Place into the preheated oven for 1 hour and 15 - 20 minutes or until done. You'll want to place a skewer into the bundt cake and if it comes out with moist crumbs, it's done. Mine took 1 hour and 20 minutes.
Let the cake cool for about 20 minutes. Turn the cake out onto a wire rack and cool. Let cool completely.
Once cooled, add the cake to a cake plate.
In a microwave-safe bowl, add in the milk chocolate chips, peanut butter, and heavy cream. Microwave for 30 seconds and stir. Repeat microwaving for 30 seconds and stir again. If it still has some lumps, microwave one last time for 20 seconds and stir.
Add the ganache to the top of the cooled cake. The ganache will be thick. I added dollops all around the top of the bundt and then tapped the cake plate to smooth out the ganache.
I added sprinkles to the top and served!
You can substitute the gluten-free flour for all-purpose flour and leave out the xanthan gum.