Preheat and Prepare: Preheat your oven to 350°F (175°C). Grease and flour the two 9-inch round cake pans.
Mix Dry Ingredients: In a large mixing bowl, combine sugar, flour, Hershey's cocoa powder, baking powder, baking soda, and salt.
Add Wet Ingredients: Add eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Mix until well combined.
Boiling Water: Stir in the boiling water. The batter will be thin; this is perfectly fine.
Divide and Bake: Pour the batter evenly into the prepared pans. Bake for 30 to 35 minutes or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then remove and cool completely on a rack.
Prepare Chocolate Frosting: In a saucepan, melt the butter. Stir in Hershey's cocoa powder. Remove from heat and beat in confectioners' sugar, milk, vanilla extract, and a pinch of salt. Beat until smooth.
Frost the Cake: Once the cakes are completely cool, place one layer on a serving plate. Spread a layer of chocolate frosting on top. Place the second cake layer and frost the top and sides evenly.
Decorate (Optional): For an extra touch of elegance, consider garnishing the cake with chocolate shavings, chocolate chips, or a dusting of cocoa powder.