Step 1: Prepare the Cake Batter

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
2. Mix Dry Ingredients: In a large mixing bowl, combine flour, sugar, cocoa powder, baking powder, baking soda, and salt.
3. Add Wet Ingredients: Add eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Mix until well combined.
4. Incorporate Boiling Water: Carefully stir in the boiling water until the batter is smooth (the batter will be thin).
5. Bake: Divide the batter evenly among the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let cool in pans for about 10 minutes, then transfer to wire racks to cool completely.

Step 2: Make the Frosting

1. Beat Butter: In a mixing bowl, beat the softened butter until creamy.
2. Add Sugar: Gradually add powdered sugar and mix until combined.
3. Add Cream and Vanilla: Pour in heavy cream and vanilla extract; beat until fluffy and smooth. If needed, adjust consistency with more cream or powdered sugar.

Step 3: Assemble the Cake

1. Level Cakes: Once the cakes are completely cooled, level them with a knife if necessary.
2. Layer Cakes: Place one layer of cake on a serving plate or cake stand. Spread a layer of frosting on top.
3. Repeat Layers: Add the second layer of cake and repeat with frosting. Top with the final layer.

Step 4: Frost the Cake

1. Crumb Coat: Apply a thin layer of frosting around the entire cake to seal in crumbs. Refrigerate for about 30 minutes.
2. Final Frosting Layer: After chilling, apply a thicker layer of frosting around the cake, smoothing it out with a spatula.

Step 5: Decorate

1. Colorful Frosting: Divide remaining frosting into bowls and tint with food coloring (orange for Halloween).
2. Decorate: Use a piping bag to pipe decorations on top of the cake using different colors. Add sprinkles, edible glitter, and Halloween candies for extra flair.