Preheat the oven to 180C/160C Fan/Gas 4. Line and grease a 20cm/8in springform cake tin.
Cream together the butter and sugar until pale and fluffy. Beat in the eggs one at a time then add the lemon zest. Mix in the flour and pour the batter into the prepared tin. Smooth the surface and bake for an hour, or until a skewer inserted into the centre comes out clean.
For the lemon drizzle, add the lemon juice and sugar to a saucepan and warm through. Leave to cool, then brush it over the surface of the cooked cake while it is still warm. Set aside to cool completely.
For the lemon curd, whisk together all the ingredients in a saucepan. Heat gently, stirring every now and then, until thickened. Set aside to cool completely.
For the lemon buttercream, beat the butter until soft and fluffly. Add the icing sugar slowly until completely combined, pale and fluffy. Stir in the lemon extract.
Slice the cake in half horizontally and fill with buttercream and lemon curd. Place on a cake board. Spoon any remaining buttercream on top of the cake and smooth it down to completely cover the cake in a smooth ‘crumb coat’. It doesn’t need to look great at this stage, but it is important that the top and edges are straight and smooth (so that lumps don’t show through when the cake is covered with fondant icing).
For the marshmallow fondant, add the marshmallows, a tablespoon water and a little food colouring to a microwave safe bowl.
Heat in short bursts in a microwave on a medium heat, stirring well each time, until the marshmallows are melted. Stir in the icing sugar and mix until it forms a rough paste - don’t worry if there are still lumps of icing sugar at this stage.
Grease your hands and a work surface with vegetable fat. Tip out the marshmallow paste and knead until the paste is smooth. Shape it into a rough circle wrap in cling film and set aside.
Dust a clean work surface and a rolling pin with cornflour and roll out the marshmallow fondant until large enough to cover the cake with some excess.
Lift the marshmallow fondant onto the cake and smooth the top using a fondant icing smoother if you have one, or your hands. Carefully smooth down the sides, making sure you push out any air bubbles as you go. If you have any small creases rub them out using a little cornflour. Trim off any excess icing from the bottom.
If using the decorations, spray the cake with pearl lustre spray and cover the bottom edge with ribbon and secure in place. Mix 2 tablespoons of lustre dust with enough rejuvenator spirit to make a paint. Neatly brush a large gold circle on top of the cake and set aside to dry. Reserve any leftover paint.
To make the sugar flowers, knead the paste on a work surface greased with vegetable fat until pliable. Add a few drops of the colouring and knead until the paste is evenly coloured.
Cut out petal shapes and use a baller icing tool (or a round knife handle) to thin out the edges. Pull the petals together to make flowers and pinch the bottom to make them stay together. Paint the edges of the petals with gold paint. Trim off any excess from the ‘stalk’ and arrange the flowers on top of the cake.