Modelling chocolate is generally not used as a fondant or cake covering but rather as a modelling substance for creating objects, flowers, ribbons and border strips around cakes, as it is a slightly tougher and sturdier substance than other forms of chocolate. However, it can be made in large quantities, rolled flat and placed over a cake. Before covering a cake with modelling chocolate, however, a "glue" layer such as a butter cream or fruit syrup icing must be spread in order for the chocolate to adhere to the cake. You can make modelling chocolate from dark, white or milk chocolate.
Melt 198gr. of dark chocolate in a double boiler or a makeshift bowl and pan boiler. Do not melt the chocolate directly on a burner or in the microwave, as it will turn to chalk. While you are melting the chocolate, stir it continually until it is completely melted and smooth. Remove the pan or bowl to the counter and allow it to cool slightly.
Stir ¼ cup of corn syrup into the melted chocolate. It will start to stiffen with the chocolate immediately, so you must stir from the moment the corn syrup interacts with the chocolate. Stir until the corn syrup is completely incorporated. Transfer the chocolate to a large plastic zipper bag and place in the refrigerator for two to three hours.
Frost the cake in the meantime. As with fondant or marzipan coverings, in order for the chocolate cover to stick to the cake, there must be a "glue" layer. Spread a thin layer of butter cream, fruit syrup or other sticky icing you prefer over the entire outer surface of the cake. Place on a cake plate and set aside.
Spray the counter with cooking spray or rub with oil in order to prevent the modelling chocolate from sticking. Remove the chocolate from the refrigerator and knead it on the counter until it is pliable (when it reaches room temperature). Roll it into a ball and pat it flat.
Using a metal or wooden rolling pin, roll the modelling chocolate into an even circle large enough to cover the entire cake . Place the rolling pin in the middle of the flattened chocolate and flip the chocolate over it in order to transfer it to the cake. Gently slide the chocolate off and onto the cake. Using your hands or a cake trowel, press the chocolate firmly into the cake to adhere to the icing. Flatten all the sides and trim away any excess chocolate that hangs over the bottom edge.
Modelling chocolate is already a little tougher than other cake coverings such as fondant or marzipan, therefore you do not want to let it sit too long. For the freshest result, make and consume the cake within 24 hours.