Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Add the sugar and mix until combined.
In a separate bowl, whisk the eggs, milk, oil, and vanilla until smooth. Pour the wet mixture into the dry ingredients and beat on medium speed for about 2 minutes until well combined.
Carefully stir in the boiling water; the batter will be thin but that's normal. Pour the batter evenly into the prepared cake pans.
Bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean. Remove from oven and let the cakes cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.
In a large bowl, beat the softened butter until creamy and pale. Gradually add the confectioners' sugar, mixing well after each addition. Mix in vanilla and beat until fluffy. If desired, tint the frosting black for web decoration.
Place one cake layer on a serving plate and spread an even layer of frosting over the top. Top with the second cake layer and apply a thin crumb coat all over the cake. Chill for 30 minutes to set the crumb coat.
Apply a final thick layer of frosting smoothly around the cake's surface, creating an even finish. Chill the cake again for 20 minutes to firm up the surface.
Transfer the black icing or gel into a piping bag fitted with a small round tip. Starting at the center of the cake's top, pipe outward concentric circles to form a web pattern. Use a toothpick or skewer to gently draw lines from the center to the edges, connecting the circles to complete the web.
Continue to refine the web pattern, making sure the lines are clean and evenly spaced. Chill briefly if needed to set the design.
Once the web is complete, transfer the decorated cake to a serving platter. Slice and enjoy your spooky, web-themed chocolate cake!
