Pulverize 10-12 digestive biscuits with 2 Tbs melted butter, press into a 23cm springform pan and bake in a 180°C oven for 10 minutes.
Let cool. For the filling, beat together 1 kg ricotta, 150g caster sugar, 40g plain flour, 5 eggs, ¼ tsp salt, 2 tsp vanilla extract and the
grated zest of an orange. Pour into the pan and bake in the oven at 170°C for about 1 hour. Remove and let cool, before running a thin knife
around the edge and removing from the pan. For the topping, melt 2-3 Tbs marmalade with the juice of ½ a lemon, simmer until thick and syrupy,
then spread over the top. Chill for an hour before serving.