Preheat oven to 150C. Grease and line a 23cm springform cake pan with baking paper. Line a baking tray with paper towel. Put cake pan on prepared tray. Combine raisins and cranberries in a large bowl. Slice the bread and spread butter on one side of each slice of bread.
Line base of cake pan with bread, butter side down. Sprinkle a half of the fruit mix over brioche. Top with another layer of bread and fruit. Repeat once more, finishing with a layer of bread.
Whisk eggs, cream, milk, sugar and vanilla in a large bowl. Slowly pour egg mixture over pudding, allowing it to seep in. Stand for 30 minutes. A small amount of liquid will drizzle from cake pan and be absorbed by paper towel. Discard paper towel and rinse tray. Replace cake pan on tray.
Bake pudding for 75 minutes or until a skewer comes out clean when inserted in the centre. Stand for 15 minutes. Release clamp on cake pan and transfer pudding to a wire rack to cool. Serve warm or cold with whipped cream.