For the Chocolate Cake:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment paper.
2. Mix Dry Ingredients: In a large bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk to combine.
3. Combine Wet Ingredients: In a separate bowl, beat the eggs. Add in the milk, vegetable oil, and vanilla extract, and mix until smooth.
4. Mix Dry and Wet Ingredients: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
5. Add Boiling Water: Slowly pour in the boiling water, stirring continuously. The batter will be thin but this will result in a moist cake.
6. Bake: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

For the Vanilla Icing:

1. Beat Butter: In a large bowl, beat the softened butter on medium speed for 2-3 minutes until smooth and creamy.
2. Add Powdered Sugar: Gradually add the powdered sugar, one cup at a time, beating on low speed. Scrape down the sides of the bowl as needed.
3. Add Vanilla and Cream: Once all the sugar is incorporated, add the vanilla extract, heavy cream, and a pinch of salt. Beat on medium-high speed for 2-3 minutes until light and fluffy. Adjust the consistency with more cream (for a thinner icing) or more powdered sugar (for a thicker icing).

Assembly:

1. Level the Cakes: Use a serrated knife to level the tops of the cakes if necessary.
2. Frost the Cake: Place the first cake layer on a serving plate. Spread a thick layer of vanilla icing on top. Place the second cake layer on top and apply a thin crumb coat around the entire cake. Refrigerate for 30 minutes.
3. Final Frosting: Apply a thicker layer of icing over the crumb coat, smoothing it with an offset spatula. Decorate with chocolate shavings, sprinkles, or fresh fruit as desired.