Preheat oven to 180C/350F and grease and lightly flour 2 nine-inch cake pans and 2 6-inch cake pans (or you can use one pan and slice the layers)
In the bowl of a stand mixer, mix together all the dry ingredients
To the dry mixture, add the eggs, vegetable oil, milk and vanilla and mix on medium speed until well combined.
Reduce the speed to as low as it will go and add the boiling water.
Increase speed to high and beat for one minute.
Distribute the cake batter evenly between the cake pans and bake for 24-35 minutes depending upon the size of the pan or until a skewer inserted in the center of the cake comes out clean.
Remove from oven and cool on a rack for 5-10 minutes and let cool completely before icing.
Vanilla Buttercream
In a mixer, cream the butter 3-5 minutes until light and smooth
Add half a cup of icing/confectioner's sugar and beat until incorporated and then add another half cup until all sugar has been used.
Increase mixer speed to high and beat for a minute and then add the vanilla and salt and beat until combined.
Add the milk until the icing is of the consistency you prefer. For softer icing use more milk, for stiffer icing (for piping) use more icing sugar/confectioner's sugar.
Chocolate Buttercream
In a mixer, cream the butter and sifted cocoa powder 3-5 minutes until smooth
Add icing/confectioner's sugar and milk to cocoa mixture by adding 1 cup of sugar followed by about a tablespoon of milk. After each addition has been combined, turn mixer onto high speed for about a minute. Repeat until all sugar and milk have been added.
Add vanilla extract and combine well.
If frosting appears too stiff, add more milk, a tablespoon at a time until it's the consistency you want. If it appears too wet and does not hold its form, add more icing/confectioner’s sugar, a tablespoon at a time until it reaches the right consistency.
Assembly
Level the layers and spread vanilla buttercream between the layers
Spread chocolate buttercream on the top and sides.
Pipe icing on the bottom and where the top tier starts (it covers a myriad of sins)
Make chocolate curls or chocolate shavings for the top.
Sparklers are optional :)
Recipe by Orgasmic Chef at https://orgasmicchef.com/two-tier-chocolate-birthday-cake/