Grease and line two 18cm (7inch) square cake tins.
Put the margarine with the sugar in a large mixing bowl and whisk until pale and light in texture.
Gradually whisk in the eggs, one by one, then stir in the lemon extract.
Sift in the flour and baking powder and fold together.
Spoon the batter into the prepared tins, sharing equally between them and level off.
Bake for 10-12 minutes until risen and firm to the touch, then turn on to a wire rack to cool completely.
Make the buttercream
Put the softened butter in a mixing bowl and whisk until creamy and pale.
Sieve in the icing sugar then whisk again, starting slow and speeding up until you have a smooth, spreadable icing
Assemble the sponges
Trim the tops of your sponge as sparingly as possible to remove the crust.
Spread a thin layer of buttercream onto one sponge and place the other on top to form a neat sandwich.
Trim the edges to give a sharp square. You can use a ruler to help you do this accurately, then ut into 16 neat squares in a 4 x 4 pattern.
Cover your sponges with marzipan
Set aside 150g (5oz) of marzipan - you'll use this for the tops later.
First, you're going to make strips to go around your cakes.
Measure the height of your cake squares - this is how wide your strips need to be.
Now measure all the way around the outside of a square - this is how long your strips need to be plus a centimetre or two (half an inch) to allow for variation.
Split your marzipan in half and work with one piece at a time. You need to roll it out thinly enough to give 8 strips from each piece.
When you've rolled out and cut both halves of marzipan, you should have 16 strips in all.
Spread a marzipan strip with a thin layer of buttercream.
Place a square of cake on its side aligned with one end of the strip.
Now carefully roll up so that the strip wraps around the outside of a cake. Trim off any excess at the end with a sharp knife.
Repeat for all 16 cakes.
Now spread the exposed top of each cake with a thin layer of buttercream.
Roll out the reserved marzipan thinly and cut out 16 squares to cover the tops of the cakes.
Use your fingers to gently smooth the marzipan all over to ensure a neat finish and no gaps or open seams.
Add the buttercream topping
Transfer all of the remaining buttercream into a piping bag.
Snip off about 1cm (½ inch) from the end of the bag and pipe a neat blob on top of each cake.
Place your cakes, well spaced, on a wire rack over a tray and put the tray in the fridge to chill for 30 minutes to firm up. Don’t skip this step as it’s necessary to get a good end result.
Ice your fondant fancies
Put the chopped white icing in a saucepan and add 45ml (3 tbsp) water.
Heat very gently, stirring occasionally, until melted together. Add up to 15ml (1 tbsp) more, if needed.
Remove from the heat and add the lemon extract and a few drops of yellow food colouring.
Stir until you have an even colour, adding more colouring if necessary. I like to make my icing as similar to the marzipan shade as possible so that any imperfect patches would be unlikely to show later.
Remove your cakes from the fridge and spoon the liquid fondant over the cakes to coat the top and sides.
The cold cakes will cause the icing to set quickly, making it tricky to patch, so I find it better to concentrate on getting one cake neat and then moving onto the next, rather than pouring the whole lot of icing all at once and then having to rush to neaten them.
You can use a palette knife to quickly cover any bare areas. If the icing sets in the pan, you can place it back on the hob to gently re-melt.Fix a mini icing flower to the top of each cake.
To serve, carefully trim the icing drips from the bases of the cake and place on a serving plate.
Video
Notes
Note: lemon extract can vary in strength. Taste the icing and add more, if desired, before pouring over the cakes.