Cake decorating television shows reveal a variety of bakery genius. From sprinkles to sculpted fondant, cake decorations achieve new and innovative designs all the time. The essential part of an 18th birthday cake is the personality of the teenager. Perhaps, sprinkles and candles are all you really need to decorate her cake. If you want to work with something different and create a special cake, then fondant is a versatile, sugary coating for decorative baked goods.
Write down a list of things that your teenager likes, such as a sport, television show, movie, hobby or music. Pick out three colours that she likes. From the list and colours, think of a theme, such as a pink iPhone cake for a girl who loves her phone.
Bake a traditional cake in a rectangle or circle cake pan, depending on the shape of the cake. For guitar-themed cakes or other special shapes, see if cake stores sell a pan for your design online or at a bakery. For the iPhone example, you need to shape the base into a vertical rectangle with rounded corners.
Set down a large piece of cake board covered in waxed paper on a flat surface. Remove the cake from the pan and place it onto the waxed paper. Cut and shape the cake with a knife into the design you need. In this example, modelled after the iPhone, cut the corners to a rounded shape.
Ice all surfaces of the cake lightly with buttercream icing and a spatula. You only want a thin layer of icing to go between the cake and fondant topping.
Knead a large piece of fondant until pliable and soft to cover the cake. If you want to add colour, work in gel food colouring as you knead. For the pink iPhone example, pre-coloured pink fondant is available, or if you want to create a different colour, then use food colouring, such as black gel food colouring to create the iPhone face in the centre of the cake.
Dust a wooden board or marble slab with icing sugar, then place the ball of kneaded fondant in the centre. Press a rolling pin into the fondant to smooth it out. Sprinkle confectioners' sugar into the fondant if it sticks to the rolling pin.
Roll the fondant around the rolling pin. Bring the rolling pin to the cake's bottom edge and unroll the fondant to cover the top of the cake. For example, smooth the fondant with your palm along the top of the cake to create the pink base for the iPhone case. Use a knife to trim off excess fondant.
Add other layers of fondant icing to create the rest of the theme cake. For the iPhone, use another piece of fondant to create the face of the iPhone in black. For best results, use a picture of your subject to copy, then create each piece with fondant, which you cut into sizes and shapes necessary for the cake.
Place 18 candles around the cake's edge once finished or purchase a pre-made number 18 cake candle from the grocery store. Sprinkles and other sugary decorations also come pre-made, so consider adding some of your teenager's favourites if the design allows.