Soak the sultanas in the lemon vodka overnight.
For the base, crush the crackers into a bowl. Add the melted butter and icing sugar and stir to combine.
Press the biscuit mixture into the base of a 23cm/9in spring-form cake tin.
Preheat the oven to 180C/355F/Gas mark 4.
For the topping, place the ricotta, the cream cheese, eggs, sugar and vanilla seeds into a food processor and blend until combined and smooth.
Transfer the cheese mixture to a clean bowl. Drain the sultanas from the vodka and add the sultanas to the cheese and mix well.
Spoon the cheese mixture onto the biscuit base and sprinkle over the poppy seeds to completely cover the top.
Transfer to the oven to bake for one hour. The surface should still be a little wobbly in the very centre of the cheesecake when it is done. It will firm up as it cools.
Once it is cooled, serve slices of the cheesecake onto plates with a dollop of vodka whipped cream.