Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, combine flour, cocoa powder, sugar, baking powder, baking soda, and salt. Whisk until evenly mixed.
Add eggs, milk, oil, and vanilla to the dry ingredients. Beat on medium speed for 2 minutes.
Stir in boiling water until the batter is smooth. The batter will be thin.
Pour the batter evenly into the prepared cake pans.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow cakes to cool in pans for 10 minutes, then remove from pans and transfer to a wire rack to cool completely.
Once cooled, place one cake layer on a serving plate. Spread a layer of icing on top. Add the second layer of cake.
Melt the white chocolate or prepare icing and place it in a piping bag. Pipe a spiral design on top of the cake.
Use a toothpick to drag lines from the center of the spiral outward to create a spiderweb pattern.