Preheat the oven to 180°C. Lightly grease a 23cm springform cake tin and line with baking paper.
To make the base, put the amaretti and digestive biscuits in a large sealable bag and crush with a rolling pin until fine crumbs. Tip into a bowl, add the butter and mix until all the crumbs are coated. Transfer to the prepared tin and spread evenly over the base. Bake for 10 minutes. Remove from the oven and allow to cool. Reduce the oven temperature to 160°C.
To make the filling, lightly beat the eggs and sugar until the sugar has dissolved. Add the ricotta, mascarpone, flour and lemon zest and squeeze of juice and continue beating until well combined. Pour the filling over the biscuit base. Bake for 45 minutes, or until just set with a slight wobble in the middle. Switch off the oven, open the door a little and leave the cheesecake in oven to cool completely.
For the caramelised oranges, grate the zest of 1 orange into a small pan with the sugar, cinnamon stick and 1/4 cup water. Heat over a medium heat, stirring until the sugar has dissolved then simmer without stirring until the sugar turns a deep caramel colour. Remove from the heat and carefully pour in another 1/4 cup water. Stir until any caramel lumps have melted.
Set aside to cool.
Peel the oranges and slice them into rounds. Use to top the cooled cheesecake. Spoon over some
Caramel sauce just before serving.