A mousse ring is like a springform tin without a base; you can buy them at good kitchen shops, or just use a greased and lined springform cake tin.
Preheat the oven to 170C/gas 3. Make a shortbread base by beating the butter, sugar and vanilla seeds together in a large bowl until smooth. Add the flour to the mix and beat until it comes together in a ball. Press into the bottom of a 25cm mousse ring, then place on a lined baking tray and bake in the oven for 15–20 minutes, until golden. Leave the oven on.
To make the filling, combine the sugar, vanilla seeds, cream cheese and cornflour in a bowl and mix until smooth. Stir in the eggs, then the cream, until combined. Pour the filling over the shortbread base and bake in the oven for 45–55 minutes, until the filling has just the slightest wobble.
For the topping, put 300g cranberries in a saucepan with the lemon juice, sugar and 50ml water and simmer for 5–10 minutes over a medium heat, or until the cranberries break down and the mixture thickens. Stir in the rest of the berries, then leave to cool slightly, before pouring over the cheesecake. Chill it in the fridge. When ready to serve, carefully remove from the tin and slice.