Preheat oven to 180°C. Grease 23cm round cake pan with butter; lightly sprinkle with flour.
Beat cake mix, oil, water, coffee and eggs in large bowl with electric mixer on low speed until moistened. Beat on medium speed 2 minutes. Pour batter into cake pan.
Bake 40 to 45 minutes or until toothpick inserted in center of cake comes out clean. Cool 10 minutes in pan. Remove from pan to cooling rack to cool completely.
Heat 1150ml milk to boiling in medium saucepan over medium-high heat. Add crème caramel mixes; heat to boiling again, stirring constantly, until powder has fully dissolved. Transfer to heatproof bowl; cool 30 minutes.
Break cooled cake into pieces; place in 3-liter serving dish. Pour crème caramel over cake; let stand 30 minutes, then cover with plastic wrap and refrigerate about 2 hours or until set.
Beat whipping cream mixes and 230ml cold milk in large bowl as directed on package.
Spread whipped cream on top of pudding; sprinkle with chopped pistachio nuts.