Step 1: Preheat your oven to 350°F (175°C). Prepare two 9-inch round cake pans by generously greasing and flouring them, or line the bottoms with parchment paper for effortless release.
Step 2: In a large mixing bowl, combine all the dry ingredients for the cake: the all-purpose flour, Hershey’s cocoa powder, granulated sugar, baking powder, baking soda, and salt. Whisk these ingredients thoroughly to ensure they are well combined and lump-free.
Step 3: Add the wet ingredients – eggs, milk, vegetable oil, and vanilla extract – directly into the bowl with the dry mixture. Using a hand or stand mixer, beat on medium speed for approximately 2 minutes until the batter is smooth and evenly blended.
Step 4: Carefully pour in the cup of boiling water. Stir gently until it is just combined into the batter. Don't worry if the batter appears thin; this consistency is crucial for an incredibly moist cake.
Step 5: Divide the prepared batter evenly between your two prepared cake pans. Bake for 30–35 minutes, or until a wooden skewer or toothpick inserted into the center of a cake comes out clean.
Step 6: Allow the cakes to cool in their pans for about 10 minutes before gently inverting them onto a wire rack. Let them cool completely before attempting to frost. This prevents the cake from breaking and ensures the frosting adheres properly.
Step 7: In a medium bowl, combine the softened unsalted butter and Hershey's cocoa powder. Beat them together until the mixture is smooth and fluffy, indicating a good base for your frosting.
Step 8: Gradually add the powdered sugar, alternating with the milk, beating continually. Continue beating until the frosting is light, fluffy, and perfectly smooth. Stir in the vanilla extract. Adjust the consistency by adding more milk for a thinner frosting or a bit more powdered sugar for a thicker one.
Step 9: Place one completely cooled cake layer on your chosen serving plate or cake stand. Spread a generous, even layer of the creamy chocolate frosting over the top. Carefully place the second cake layer on top, then proceed to frost the top and sides of the entire cake. Use an offset spatula to create smooth sides or elegant swirls, whichever you prefer.