In the bowl of the stand mixer at medium speed, cream together the shortening and butter until smooth.
Add the vanilla extract and melted chocolate and stir until thoroughly combined.
Add the sifted confectioners sugar, one cup at a time, scraping down the bowl between each addition.
Add the milk one tablespoon at a time, just until the frosting is creamy, not runny. You may not need all the milk. Whip at medium speed for about 1 minute to combine all the ingredients thoroughly.
Use promptly or refrigerated with plastic wrap pressed onto the surface. Allow to come to room temperature and whip again before using.
Chocolate Buttercream (no shortening)
Stir together the melted chocolate, vanilla, and salt in a bowl until the salt dissolves.
In a stand mixer with paddle attachments, beat the butter until it is smooth, about 30 to 60 seconds. In a bowl, whisk together the confectioners sugar and cocoa powder. Reduce the mixer speed to low, then slowly add to the butter, beating until smooth, 2 to 5 minutes.
Beat in the melted chocolate mixture. Increase speed to medium-high and beat until fluffy, 4 to 8 minutes.
Make the vanilla frosting recipe. Set aside approximately ¼ cup, then divide the remaining frosting into two equal parts. Tint the two larger portions green and orange and the smaller portion red.
Place the large cake on the serving platter. Cut the smaller cake into three roughly oval shaped chunks.
Use some of the frosting, whichever flavor or color you choose, to anchor the volcano layers to the base. (We used green so it would show up in the photos.) Use the serrated knife to shape and form the volcano and base to your liking. We used some of the shaved cake pieces to create a cone at the top of the volcano by piling them around the edge.
Spread the chocolate frosting around the volcano, bringing it up and over the lip of the cone, and around parts of the base. The frosting doesn’t have to be neat, this is a rocky, craggy volcano after all.
Scrape the chocolate frosting with a fork to create texture.
Begin spreading the green frosting around the rest of the base. Again, we didn’t go for smooth, wanted it to give the impression of tropical undergrowth.
Prepare one piping bag with orange frosting using the #16 tip. Pipe the frosting (lava) into the cone and down the sides in whatever pattern and direction you like. Michael decided to take out one of the dinosaurs with the orange lava. Add some red lava frosting by dipping the toothpick into the frosting and just twisting it on top of the orange here and there.
Change the orange frosting tip to the #3. Pipe Happy Birthday and the child’s name on the open area on the platter/baking sheet. Place candles in the volcano cone’s pool of lava.
You can find this recipe at https://andreasrecipes.com.