Method

1. To make the bottom-tier cake, heat oven to 180C/160C fan/gas 4. Grease and line a 23cm cake tin with baking parchment. Put 250g of the butter and 250g sugar in a large bowl and, using an electric hand whisk, cream until light and fluffy. Add 4 eggs, one at a time, beating well after each addition. Fold in 250g of the flour, 1 tsp lemon extract, and the zest of 1 lemon until you have a smooth batter. Spoon into the tin and smooth the surface. Bake for 40 mins or until a skewer poked into the centre comes out clean. Leave to cool in the tin for 10 mins, then turn out onto a wire rack, remove the parchment and cool completely. Repeat with the remaining half of the ingredients, so that you have 2 large cakes.

2. Meanwhile, make the icing for the bottom tier. In a large bowl, beat the butter with a quarter of the icing sugar. When fully combined, add the rest in 3 additions, beating between each. When the icing is smooth, add the milk, zest and juice, and curd, then whisk until fluffy. Set aside until needed, or chill, but bring to room temperature before using.

3. Now make the top tier. Heat oven to 180C/160C fan/gas 4 (if not already on). Grease and line a 15cm cake tin with baking parchment. Cream together the butter and sugar until light and fluffy. Add the eggs, one at a time, beating well after each addition. Fold in the flour and extract until you have a smooth batter. Transfer to the tin, smooth the surface and bake for 20 mins, then reduce the oven to 160C/140C fan/gas 3 and cook for a further 25 mins. Remove from the oven and allow to cool in the tin for 10 mins, then turn out onto a wire rack, remove the parchment and cool completely.

4. To make the icing for the top tier, cream the butter and 100g icing sugar together until smooth, then gradually incorporate the rest. Add the milk and strawberry powder, then whisk thoroughly until light and fluffy.

5. When the larger cakes are completely cool, slice each in half horizontally so that you have 4 sponge layers. Using a 10cm cutter, cut a hole in the centre of each of the lemon sponges for the bottom tier. Sandwich the 4 sponges together on a cake stand, using the lemon buttercream, then cover the whole cake in a thin layer of the remaining lemon icing. Put in the fridge for a minimum of 2 hrs to firm up.

6. When completely cool, slice the small top tier cake horizontally so that you have 3 sponge layers. Use the strawberry buttercream to sandwich them together on a chopping board, then use the remaining strawberry icing to cover the outside. Leave in the fridge for a minimum of 2 hrs to firm up while you ice the bottom tier.

7. Now start to make the pale blue icing. Dust your work surface with a little icing sugar. Knead a little blue food colouring into 1.5kg fondant icing until it’s an even colour. Remove 500g, wrap in cling film and set aside for the top tier. Roll out the remaining 1kg to a circle wide enough to cover the bottom tier – you can check this with a piece of string. Gently roll up your fondant onto your rolling pin and unfold onto your cake. Smooth the icing on the outside with your hands, then trim off the excess at the bottom. Cut a small cross in the centre of the fondant where the hole sits and push the remaining fondant carefully onto the inside of the hole, trimming any excess. Fill the centre with sweets of your choice. Place the 4 dowels into the cake at 3, 6 and 9 and 12 o’clock, just next to the hole in the middle, then trim so they are flush with the cake.

8. Cover the top tier cake in the remaining blue fondant in the same way, then mount onto the bottom cake, enclosing the sweets. Transfer the icing glue to a small piping bag and snip off the end. Use to pipe a drizzle of icing around the base of each tier. Place pearlescent or silver balls around the base of each cake to cover any rough edges.

9. To make the balloon decorations, divide the remaining 500g of fondant into the number of colours you are using. Use different food colourings to colour each piece of fondant. Roll out on a surface dusted with icing sugar and, using small cookie cutters, cut out circles of fondant. Use the icing glue to stick the balloons onto the cake. Decorate with colourful candles. Will keep for up to 3 days.