Fondant is an ideal icing to use to make a cake resemble a tomato because it creates a perfectly smooth surface on the cake. Fondant comes in a variety of colours and in varieties that you can roll or pour. Because decorating a tomato-themed cake involves using a cake that was baked in a spherical pan, it is best to use poured fondant that will automatically contour to the surface of the cake.
Cover the entire top surface of the spherical cake with a layer of buttercream icing. Allow the buttercream to harden for about 15 minutes.
Pour the red fondant over the top of the cake, starting in the centre and allowing the icing to drip evenly down the sides of the cake, fully coating the cake. Let the fondant dry. If you need to apply several coats, allow the fondant to dry in between. Touch up any bare spots with a spatula.
Set the cake aside while you design the leaves and stem for your tomato shaped cake.
Sprinkle a small amount of icing sugar on your work surface and roll out the green fondant to a thickness of about ¼ inch. Score out the shape of a tomato leaf cluster with a sharp knife. Look at a real tomato to get an idea of how the leaves are shaped. Cut out the shape and paint a thin layer of water on its underside so that it will adhere to the cake, then set it on top of the cake.
Form a small bit of green fondant to act as the stem for the tomato. Apply a small amount of water to the end of the stem and attach it to the top centre of the leaf cluster to finish the tomato.