For the cake
- 250g butter, softened
- 250g caster sugar
- 4 eggs
- 300g self-raising flour, sieved
- 150ml natural yoghurt
- ½ tsp baking powder
- 100g white chocolate, finely chopped
For the royal icing
- 1 egg white
- 225g icing sugar, sieved
- Preheat the oven to 150°C/Gas 2. Grease a 23cm pushpan with Cake Release or softened butter.
- In a mixing bowl beat the butter and sugar until soft with an electric whisk. Gradually beat in the eggs, adding a spoonful of the flour between each addition. Add the yoghurt and beat for a few seconds until combined, then fold in the remaining flour, baking powder and white chocolate.
- Spoon the cake mixture into the tin, level with the back of the spoon then bake for 55-60 minutes until well risen and firm to touch. To check that the cake is cooked insert a skewer into the centre of the cake it should come out clean. Allow the cake to stand in the tin for 10 minutes then push out and leave to cool completely on a wire rack.
- Meanwhile, make the royal icing. Whisk the egg white in a bowl until frothy then add the icing sugar a spoonful at a time, beating until the mixture is firm. Set aside.
- To make the bubbles, use your fingertips to roll all of the moulding paste into tiny balls, the largest the size of a garden pea. Place on a tray lined with parchment paper to dry.
- Slice the cake horizontally using a serrated knife. Spread half of the frosting on the flat surface of one cake and sandwich together. Add one of the rods to the base plate of the anti-gravity kit, gently lower the cake down over it then add the second rod and a corner piece. Cover the cake in the remaining frosting and use a palette knife to smooth the top and sides.
- Roll out the white icing on a flat surface lightly dusted with icing sugar until you have a 36cm circle. Make a small incision with a knife to help it fit over the rod then lower over the cake. Use your hands to smooth the top and sides then remove any excess icing with a sharp knife.
- Take the empty bottle, gently push it onto the angled rod and secure with a little of the royal icing.
- Use some more royal icing to build up a shape that resembles the flow of champagne on top of the cake. Place the remaining royal icing into a piping bag and use small beads to attach the bubbles to the rod and the surface of the cake.
- Secure two evenly spaced strips of black ribbon round your cake using royal icing, and attach the gold ribbon to the edge of the base plate.
- Dust the bubbles with Edible Silk Metallic Gold Treasure using a food-safe brush and, if desired, sprinkle some edible gold stars over the surface to finish. We chose a star decoration to top our cake off but you can add whatever finishing touches you prefer to yours.
Tips: Placing a small amount of frosting on the cake board will help to secure the cake so that it does not move too much when being decorated. For a stronger gold colour on the bubbles, brush them 2-3 times.