1. Preheat oven to gas mark 4 (180° C).

To make the biscuit base

1. Butter the base of a 20cm cake tin.
2. Crush the digestive biscuits - I put them in a bowl and whack them with the end of a rolling pin.
3. Melt the butter and mix with the crushed biscuits.
4. Press the biscuit/butter mix into the cake tin and bake for 10 minutes, or until it looks ready.

While the base is baking, make the filling.To make the filling

1. Melt the chocolate.
2. Using a hand mixer, beat the cream cheese, ricotta, sour cream, vanilla essence and sugar until smooth.
3. Beat in the cornflour and the melted chocolate.
4. Beat in the eggs, one at a time.

Putting it all together

1. Wrap the base of the cake tin in foil and place it into a roasting tin.
2. Pour the filling into the cake tin.
3. Fill the roasting tin with boiling water (the foil will stop the water going into the tin - hopefully!).
4. Bake at 180C for 15 minutes and then reduce the temperature to 160C then bake for about 45 minutes more, or until it's ready (the middle of the cheesecake should still wobble).
5. Turn off the oven but leave the cheesecake in there to cool, with the door slighlty open.
6. Transfer to the fridge to cool overnight.

Eat