2-3 x 80g bags white chocolate buttons, flowers and ribbons, optional
Heat oven to 180C/160C fan/gas 4. Grease and line the base and sides of deep, round 20cm and 15cm cake tins with baking parchment - making sure the paper comes a few cms above the sides.
Boil the kettle. Put half the butter and chocolate in a pan and gently melt, stirring. Mix together half of the flour, sugar, cocoa and bicarb with a pinch of salt. Whisk 2 of the eggs and 200ml buttermilk together. Scrape the melted chocolate mixture and egg mixture into the dry ingredients. Add 150ml boiling water and whizz everything together with an electric whisk until lump-free. Divide between the tins and bake for 40-45 mins, swapping round after 30 mins if they’re on different shelves (the 15cm one should be done after 40 mins). To test they’re cooked, push in a skewer and check it comes out clean. Cool the cakes in their tins.
Repeat steps 1 and 2 again, so you end up with 2 x 20cm cakes and 2 x 15cm cakes.
Melt the white chocolate in a bowl over a pan of barely simmering water. Beat together the butter and icing sugar, then beat in the white chocolate. When the cakes are cool, split each one in half. Use the icing to sandwich back together so you end up with 2 x four-layered cakes. Sit the 20cm cake on your serving plate and spread some more icing over the top. Sit the smaller cake on top of that, and completely cover with icing. Decorate with the chocolate buttons.
If you want to add some flowers choose something edible, like roses. Make a posy, wrapping the stems in a little damp kitchen paper then some cling film, add a ribbon and add to the cake on the day of the wedding.