Preheat the oven to 180C/160C Fan/Gas Mark 4. Grease and line 2 spring-form circular cake tins (1 x 15cm and 1x20cm), allowing the baking paper to extend 3cm above the top of each tin.
Put all the ingredients for the cake in a very large bowl and beat with an electric whisk for 3-4 mins until smooth. Divide between the cake tins, about ⅓ (590g) of the mixture into the smaller tin and the rest in the larger tin. The mixture should fill the tins about halfway.
Bake on the middle shelf of the oven for 1 hr to1hr 15 mins or until a skewer inserted into the centre of the cakes comes out cleanly. The smaller cake should be ready about 10 mins before the larger cake.
Cool the cakes in the tins for 10 mins, then turn out and allow to cool completely on wire racks.
Using a serrated-edged knife, cut each cake in half horizontally so you have4sponge circles. Trim the tops of the cakes to level them, if necessary.
To decorate, first make the buttercream. Beat the butter until soft. Add the icing sugar, lemon extract and 1tbsp of the milk and whisk into the butter, starting on a slow speed and gradually increasing to high. Beat for 5 mins, slowly adding the rest of the milk, until the mixture is pale and fluffy.
Beat the raspberry jam in a separate bowl to loosen it and smooth out any lumps.
Spread the tops of 1 larger sponge and both smaller sponges with a little of the buttercream. Spread over the jam, leaving a 3cm border around the edge.
Put the larger iced cake on a cake stand or plate, iced side up, then top with the 2 smaller cakes. Finish with the un-iced larger cake on top.
Beat a generous squeeze of the blue food gel into the remaining buttercream until combined evenly, adding a little more gel if you want a really vibrant colour.
Using a palette knife, spread the blue buttercream over the top and sides of the cake until well covered. Use the palette knife to bring the icing slightly over the fault line section to create a small ridge.
Press the chocolate mini eggs into the icing all the way around the central fault line section. Chill in the fridge for 20 mins.
Empty the gold glitter spray into a small cup and mix with the vodka or gin until combined. The alcohol will ‘fix’ the glitter in place. With a clean, fine brush, paint a gold line around the edge of each fault line and the top edge of the cake. If you want to make the cake alcohol free, simply dust the gold glitter over the top of the cake instead.
You can store the decorated cake in an airtight container for up to 3 days.