Spread the rest of the buttercream over, starting with the top, then smooth and paddle it around the sides and down to the board. Repeat the whole process with the remaining cakes, using the corresponding boards and the different quantities of buttercream. The cakes are now ready to be iced. You can leave them overnight if needed, loosely covered with cling film. COVERING THE CAKE WITH ICING: You will need about 500g icing for the 15cm cake, 1kg for the 23cm cake and 1.7kg for the 30cm cake. Dust the work surface with icing sugar, knead the icing until pliable, then use your rolling pin to roll it into a circle large enough to cover the sides and top of the cake, with a little left over. Use string to check the size. Use your rolling pin to help you lift the icing over the cake. Smooth the icing around the cake with your hands, easing it over the edges and down to the board. Then trim off the excess with a sharp knife, flush with the bottom of the cake board. Smooth any marks with the flats of your hands, buffing the icing to a slight shine.Once you've iced all the cakes, cover the thick base board. Lightly brush with cooled boiled water, then lay the icing over. Trim to the edge of the board with a knife (I tend to do this like I would a pie crust, holding the board in my left hand, and knife in my right), then leave the board and the cakes to dry overnight. STACKING THE CAKES: Dowels, which are basically plastic sticks, provide stability and strength to tiered cakes, and polystyrene blocks allow you to add a 'floating' layer of flowers. By measuring and cutting the dowels to the same length as the polystyrene, you'll provide an even platform for the next cake to sit on, even if the cake below is a bit wonky. Sit the 15cm dummy centrally on top of the biggest cake. Insert four of the dowels into the cake, around the outside of the dummy, in a square shape. Push them right down until they meet the cake board. Mark with a pen where the top of the dummy comes to. Carefully pull out the dowels; then, using scissors, score around each dowel where you marked it. Snap the plastic cleanly. Re-insert the dowels in their original holes, rounded end down. Repeat the process with the 23cm cake and the 12cm dummy.Position the biggest cake in the middle of the covered board. Run a thin line of glue around the base board and fix the ribbon around it. Fix the ribbon around each cake, using a spot of the glue on the ribbon to secure it to itself. If you're moving the cake to a venue, put the cakes into their boxes now. Make a little kit to take with you - glue, scissors, etc - just in case you have to re-do anything. ON THE DAY - STACKING AND DECORATING THE CAKE WITH FLOWERS: I used hydrangeas - they're beautiful, in season and you can achieve a dramatic effect with relatively few blooms. On the day, save putting the flowers on the cake until as late as you reasonably can.