Melted butter, to grease
150ml vegetable oil
1 tsp vanilla extract
1 cup firmly packed brown sugar
1/2 cup cocoa powder
2 cups self-raising flour
1 cup chocolate chips
1/2 cup soft caramels, roughly chopped
5 cups plain flour
1 1/2 cups fine salt
1 1/2 cups water
Whipped cream, to serve
Preheat oven to 220C. Grease a 22cm round springform cake tin with melted butter and line base and side with baking paper. Separate 4 of the eggs, putting yolks in a large bowl and setting aside whites in a second large bowl. To yolks, add remaining egg, milk, oil, vanilla, sugar and cocoa, whisking until smooth.
Fold in self-raising flour until a smooth batter forms, then fold in chocolate chips and caramel. Spoon batter into prepared tin. Wrap entire tin with baking paper, then foil. Set aside.
Add plain flour, salt and water to eggwhites and mix until a smooth dough forms. Turn out onto a clean surface and roll to form a 60cm disc. Sit cake tin in centre and wrap pastry around tin to enclose completely.
Bake on an oven tray for 1 hour 10 minutes or until salt dough is dark and crisp. Remove from oven, cool for 10 minutes, then remove salt dough crust, foil and baking paper. Remove cake from tin. Dust with cocoa and serve with whipped cream.