Preheat oven to 300°F (150°C).

Grease and line a 9-inch and an 8-inch cake pan with parchment paper.

In a large saucepan, combine butter, chopped white chocolate, dark brown sugar, golden syrup, and hot water.

Stir over low heat until smooth.

Let the chocolate mixture cool.

Beat eggs and vanilla extract into the cooled chocolate mixture.

Gently fold in sifted all-purpose flour and self-rising flour until just combined.

Transfer 4 cups of batter to the 8-inch cake pan.

Pour the remaining batter into the 9-inch cake pan.

Bake the smaller cake for 1 hour and 15 minutes, or until a skewer inserted into the center comes out clean.

Bake the larger cake for an additional 15-20 minutes, or until a skewer inserted into the center comes out clean.

Let cakes cool in pans for 10 minutes.

Turn the cakes out onto a wire rack to cool completely.

Use a serrated knife to level cakes and trim sides.

Place the larger cake on a cake board, upside down.

Insert 6 wooden dowels inside the cake.

For the whipped ganache, place 18oz chopped white chocolate in a heatproof bowl.

Scald heavy cream and pour over the chocolate.

Let it sit for 5 minutes, stirring until smooth.

Cover and chill for 30 minutes, until just set.

Beat for 30 seconds until light and fluffy.

Spread the top and sides of the larger cake with ganache.

Place a small cake board on top.

Spread the board with a little ganache and top with the smaller cake.

Spread the sides and top of the smaller cake with the remaining ganache.

For the chocolate collar, cut two 3-inch-wide strips of parchment paper, 26 and 29 inches in length.

Place the strips on a flat, clean surface.

Spread the melted white chocolate evenly along the center of each paper strip.

Let it sit for 5 minutes, until partially set.

Carefully lift the corners of the larger collar and wrap around the base of the large cake.

Repeat with the smaller collar and cake.

Let the chocolate set.

Carefully peel the paper off the chocolate collars once the chocolate has set.