An erupting volcano cake rolls a cooking class and a science experiment into one. The volcano is made of cake, frosting and other sweets, and the foaming lava is made of Jell-O and baking soda—yes, this treat is completely edible. Not to mention, it puts on an impressive show.
Place a cookie sheet on a flat surface. Invert the sheet cake on top of the cookie sheet. Center the Bundt or tube cake on top of the sheet cake. If the top of the Bundt or tube cake is too wide, stack a couple layers of small sandwich cookies on top to give it some height.
Mix the food coloring into the white cake frosting to create the color of grass. Ice the sheet cake with this to turn it into a green island. Ice the Bundt cake with the chocolate frosting, or leave it as is. This will be the volcano.
If desired, add more decorative elements. Paint the area around the volcano opening with drizzles of red gel icing to simulate lava. Crush graham crackers to dust and sprinkle it around the edges of the island for sand. Fill the empty areas of the cookie sheet with blue candies like M&Ms or Skittles, for water.
Make the Jell-O according to the instructions on the packet and let it cool for about 15 minutes.
Get a small juice glass that fits snugly into the hole of the Bundt cake with the rim sitting flush with the top of the cake; set the glass on top of some sandwich cookies to raise it up, if needed. Using a funnel, fill the glass about halfway with the warm liquid Jell-O, then fill the glass almost to the top with lemon juice. Slide the juice glass into the hole in the Bundt cake.
When ready to stage the eruption, put baking soda into the juice glass and stir. The Jell-O mixture should foam up over the edge of the volcano. (This is why the fit of the glass is so important. If it sits loosely in the hole, the lava will get stuck in the hole. If the glass isn't high enough, the lava won't foam out over the top.)