Dilute the buttercream with about half-one tsp of milk or water and mix well. A lighter buttercream spreads better.
Using your spatula, cover the cake completely with the buttercream. As this is the undercoat, we don't have to worry about making it pretty.
Sprinkle your work surface with icing sugar and knead and roll out the fondant, to about 4mm thick.
Make sure your cake is very close by. Using your rolling pin,( i.e., roll about a quarter of the fondant onto the pin) lift the fondant and drape it gently onto your cake.
Using your hands, fit the fondant on the cake, lifting and draping, not pulling. Using the the side of your hands, tuck the fondant at the base of the cake.
Smooth the top with a smoother and press down around the base of the cake to mark a cutting line.
Using a small knife, cut the excess fondant off. That's it. Decorate as you fancy. Look below for the links to some of my cake creations.