Assembling an electric guitar cake takes a great deal of time and preparation. You will need a half sheet pan, which measures 45 by 32.5 cm (18 by 13 inches) and can be purchased from cake decorating supply shops. This large pan will allow you to bake a cake big enough to carve a life-size body of an electric guitar. Once you have the formed the basic shape of the guitar, use your imagination and whatever decorations or supplies you have on hand to add detail to the cake.
Carve the cake
Mix up two boxes of cake mix according to the package directions. Bake the cake batter at the temperature indicated on the cake mix box in one greased 45 cm by 32.5 cm (18 inch by 13 inch) cake pan, which is sometimes referred to as a half-sheet pan.
Remove the cake from the oven when a toothpick inserted in the centre comes out clean. Remove the cake from the pan and allow it to cool completely on a wire rack or a clean counter.
Draw the body of a guitar onto a large piece of paper. If you have an electric guitar, you can trace the guitar onto the paper to make the stencil.
Cut the drawing of the guitar out of the paper and place it on top of the cooled cake. Carefully cut around the paper with a knife until the cake resembles the body of an electric guitar.
Carefully transfer the cut cake to a large cake board or serving platter. Make sure there is enough room on the cake board to form the neck of the guitar.
Form the neck
Place 40 large marshmallows and 3-tablespoons butter in a large microwave safe bowl.
Heat the marshmallows and butter in a microwave on high for two minutes. Remove the bowl and stir the marshmallows with a wooden spoon.
Heat the marshmallows for one more minute or until they are melted. Stir the marshmallows until the mixture is smooth.
Immediately add 600 g (6 cups) of crisp rice cereal to the melted marshmallows and butter. Stir until well combined.
Pour the marshmallows onto a clean worktop and form them into the shape of the neck and head of the guitar with your hands. Refer to a real guitar or a picture of a guitar to determine the shape you want, if necessary. Work carefully as the crisp rice treats may be hot when you first begin to shape them. Allow the neck and head of the guitar to cool and then place them on the cake board to complete the shape of your guitar cake.
Decorate the cake
Ice the cooled cake with any type of frosting that is tinted to the desired colour with liquid food colouring. You can also frost the crisp rice neck and head of the guitar if you desire or leave them plain.
Roll out fondant on a surface dusted with castor sugar to prevent the fondant from sticking. Fondant can be bought ready-made from craft stores or cake decorating shops.
Use a knife to cut the shape of the guitar's scratch plate on the fondant. Refer to a real guitar or a picture of a guitar to help create a realistic looking scratch plate.
Place the scratch plate on the cake and press it gently into the frosting.
Add embellishments to the cake, such as uncooked spaghetti or shoestring liquorice for guitar strings. Mini Reese's peanut butter cups, Mentos and Junior Mints can all be used for guitar knobs.