Step 1
Preheat oven to 180C/160C fan-forced.
Step 2
Place condensed milk in a large bowl. Sift over cocoa and flour. Whisk until combined. Add milk, Kahlua, eggs and vanilla. Whisk to combine.
Step 3
Arrange half of the biscuits, in 2 layers, in a 5cm-deep, 21cm round (base) x 25cm round (top) ceramic pie dish, trimming biscuits to fill any gaps. Drizzle with half of the Nutella. Pour over half of the milk mixture. Repeat layering with remaining biscuits, Nutella and milk mixture. Bake for 35 to 40 minutes or until pie is just set.
Step 4
Meanwhile, make Marshmallow cream: Place marshmallows in a small microwave-safe bowl. Microwave on HIGH (100%) for 30 to 40 seconds, stirring halfway, until melted and smooth. Set aside to cool completely.
Step 5
Using an electric mixer, beat cream and vanilla until just-firm peaks form. Add a spoonful of whipped cream to marshmallow. Stir to combine. Fold marshmallow mixture into remaining cream until just combined.
Step 6
Working quickly, dollop warm pudding with cream mixture and drizzle with chocolate sauce, swirling gently to create a marbled effect. Sprinkle with crumbled Flake. Serve immediately.
