To cover a cake in fondant you first need to cover it in two layers of butter cream. I literally just use a icing sugar and butter mixture for this as it is only being used to prepare the surface of the cake for the fondant. The first layer of butter cream is used to create a smooth surface and should be left to crust and dry before the second layer is applied. The second layer is to make the surface of the cake slightly tacky so the fondant sticks to the cake.
Next you need to measure the sides and top of the cake and add these amounts together to work out how large a piece of fondant icing you need to roll out. Knead your fondant icing until its a workable consistency. If its a bit sticky then knead a bit of icing powder into it. Roll out the fondant so its a few millimeters thick. Measure the fondant to ensure its the right kind of size in all directions. If the fondant is a lot bigger than required then trim it down to nearer the right size as this will make it easier to transfer to the cake. When it is evenly rolled out then fold you fondant over the rolling pin and transfer to the cake.
Start smoothing the fondant down using a fondant smoother. Do not pull the fondant down on the sides as this will cause it to break, instead lift and tuck the fondant until it the surface is smooth. Once you are happy with the fondant then trim round the base and pop any air bubbles that have formed using a pin.
Hopefully your cake should look like the one above. Covering a cake with fondant is definitely a skill that you perfect over time so don't have really high expectations for your first go. If you are covering a cake for an important occasion then maybe have a practice run first. If you are unhappy with the fondant then do not try taking it off and having another go; trust me it always looks worse on the second attempt. I am still learning to cover cakes so any tips that you might have would be wonderful.
You now essentially have a blank slate and you can decorate it however you would like. I used a really easy trick to paint roses onto my cake that I will share with you in my next post (here is a sneaky preview though:)
Happy baking xxx