Preheat the oven to 180°C and grease a 20cm cake tin.
Cream butter and sugar until fluffy, then beat in eggs, lemon zest, and flour.
Bake the batter for 60 minutes or until a skewer comes out clean.
Heat lemon juice and sugar for the drizzle, then brush over the warm cake.
Whisk lemon curd ingredients in a pan and heat gently until thickened.
Make buttercream by beating butter with icing sugar and lemon extract.
Slice cake horizontally, fill with curd and buttercream, and cover with a crumb coat.
Microwave marshmallows with 15ml water until melted.
Stir icing sugar into marshmallows, then knead on a greased surface until smooth.
Roll out fondant on a surface dusted with cornflour and drape over cake.
Smooth the fondant, trim edges, and decorate with lustre paint and sugar flowers.