Preheat the oven to 180°C (160°C for fan-forced ovens).
Put the butter, cream and sugar in a large saucepan and heat gently, stirring, until the butter has melted and the sugar dissolved. Simmer for 1 minute then pour into the base of a 33 cm x 22 cm rectangular cake pan. Scatter over the chopped pecans and top with the apple slices.
Mix the cake mix and cinnamon in a large mixing bowl, add the butter, milk, and eggs. Beat with an electric mixer on low speed for 30 seconds, then on medium speed for 2 minutes (do not eat batter as it contains raw eggs). Spoon the mixture over the apples and gently level the surface with a spatula.
Place in the oven and bake for 41-44 minutes until golden, risen and just firm to the touch. Leave to cool in the pan for 10 minutes then loosen the sides of the cake from the pan with a palette knife.
Invert the cake onto a heatproof serving platter. Leave the pan on the cake for 1 minute to allow the caramel to drizzle over the cake then remove the pan.
Serve warm, cut into pieces, each one topped with a small spoonful of vanilla frosting, chopped pecans and a drizzle of caramel topping.