Preheat oven to 350ยฐF (175ยฐC) and grease and flour two 9-inch round cake pans.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add eggs, milk, oil, and vanilla extract to the dry ingredients and mix until smooth. Stir in boiling water until the batter is thin and well combined.
Divide batter evenly between the prepared pans and bake for 30-35 minutes, or until a toothpick comes out clean. Let cakes cool in pans for 10 minutes, then transfer to a wire rack to cool completely.
Heat heavy cream in a saucepan until it begins to boil. Remove from heat and pour over chocolate chips. Let sit for 1 minute, then stir until smooth to create ganache.
Place one cake layer on a serving plate and spread an even layer of creamy peanut butter on top. Place the second cake layer over it.
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