Place your unfrosted cake on top of a wire rake over a sheet pan.
Add finely chopped semisweet baking bars into a heat-resistant mixing bowl.
Heat heavy whipping cream in a saucepan just until it begins to lightly simmer, and steam is visible.
Slowly, pour hot cream over the finely chopped baking pieces. Let sit for a minute.
Using a metal spoon, slowly stir the chocolate and cream together until you get a beautiful smooth and shiny mixture.
Using the spoon, start in the middle of the cake and spoon the mixture onto the cake, add another spoonful. Using the back of the spoon gently spread and continue adding a spoonful at a time of chocolate onto the top of the cake working your way to the edges. Any excess chocolate will roll over the edge. Finish the ganache by spreading and covering the sides of the cake with the back of the spoon.
Let the cake rest while you move to the next step.
Using a double boiler, or a Pyrex mixing bowl over simmering water, add the white chocolate chips or chopped white baking bar. Let the white chocolate sit over simmering water for a minute or two. Using a fork, slowly stir the pieces together until the mixture is fully melted and incorporated. Remove from the heat.
Place the warm melted white chocolate mixture into a pastry bag. Be sure to try a couple of test strips at the bottom the of cake. Continue making strips at the top of the cake to form the “bandages” leaving room for the eyes.
When completed, place the “eyes” on top of the cake. To make the eyes, cut a large marshmallow in half and place one chocolate chip in the center.