Preheat oven to 180°C (160°C fan forced). Grease 16cm x 26cm slice pan, line base and sides with baking paper, allowing for overhang.
Beat butter, sugar and vanilla in a medium bowl with an electric mixer on medium speed for 3-5 minutes or until pale and creamy. Add egg and continue beating for a minute. Fold in plain and self raising flours, with cocoa and milk.
Spoon batter into prepared pan and spread evenly over the base. Bake for 15-20 minutes or until skewer inserted in centre comes out clean. Set aside.
Combine filling ingredients in a medium saucepan and cook over medium heat stirring constantly for 10-12 minutes or until rich caramel in colour. Remove from heat and allow to cool for 10 minutes. Pour filling over base. Refrigerate 1 hour or until firm.
Place banana slices over caramel in a single layer, top with whipped Bulla Thickened Cream followed by grated chocolate. Slice and serve immediately.