In a large mixing bowl, whisk the cream, milk, eggs, caster sugar and vanilla extract until combined.
Cut 6 hot cross buns each into 3 slices horizontally, making a bottom, middle and top. Spread the slices with 50g softened butter and sprinkle with 1 tablespoon cinnamon sugar.
Arrange bun bases into a greased oval 2L capacity ovenproof dish. Pour over a third of the egg mixture. Stand for 5 minutes. Repeat the process, standing between layers, finishing with the tops of the hot cross buns and remaining egg mixture. Sprinkle over 100g chopped white chocolate. Bake pudding for about 1 hour or until just set in the middle. Serve the pudding warm topped with blackberries.