Preheat oven to 180C/Gas 4.
1) In a flat dish, crack eggs and add milk, vanilla and cinnamon. Whisk until well combined then lay challah slices in mixture to coat and absorb it all, turning occasionally.
2) Set a 25-cm skillet, seasoned cast iron if you have, over medium heat. Add the butter and 200g sugar and cook, stirring constantly, until the sugar has melted and caramelised, about 8 minutes.
3) Whilst the sugar is melting, peel apples, core and cut into halves. Remove from heat and gently whisk in the double cream. Sprinkle in the pecans, dried cranberries and gently press in the apple halves so there is a flat surface. Lay soaked slices of challah over the top so it is completely covered - you should be able to arrange the large slices and small slices so there are no gaps. Sprinkle the top with some brown sugar and place into the preheated oven.
4) Bake in the middle of the oven for 40 to 45 minutes until the top is golden and puffy. When done, allow to cool for 2 to 3 minutes then invert onto a large plate. Dust with icing sugar, if desired, and serve.
Chef's Note: FYI - if your cast iron skillet is not seasoned, the cranberries will react with the skillet and turn black.