Pre-heat the oven to 170°C /150°C fan assisted oven / gas mark 3.
Melt the butter in a small saucepan and leave to cool for a few minutes whilst you prepare the biscuit crumbs.
Whizz up the biscuits and salt in a food processor then, with the mixer still on, pour in the melted butter until it combines with the biscuit to become a thick sandy texture.
Press the biscuit base into an 8 inch springform tin using the bottom of a glass with straight sides and push the base slightly up the sides of the tin.
Place in the oven and bake for 10 minutes.
Remove from the oven and set aside to cool slightly.
Turn the oven temperature down to 150°C / 130°C fan assisted oven /gas mark 2.
Make the filling by beating the grated cheddar with the cream cheese, sugar and cornflour (cornstarch) in a large mixing bowl or stand mixer.
Add sour cream and vanilla and mix in completely.
Add the eggs one at a time and mix until just combined.
Wrap the springform tin with two layers of aluminium foil so there are no gaps then place the wrapped tin into a slow cooker liner (see notes).
Place the springform tin in a larger baking tin with tall sides.
Pour the cheesecake mixture into the baked crust.
Pour hot water into the larger cake tin so it goes halfway up the sides of the cheesecake.
Place in the oven and bake for 1 hour.
Turn off the oven and leave the cheesecake in the oven with the door shut for 30 minutes.
Open the door of the oven so that it is slightly ajar and leave the cheesecake in the oven for another 30 minutes.
Remove the cheesecake from the oven and out of the waterbath to cool completely. Keep it still in its tin but place on a wire rack.
Finally when the cheesecake is at room temperature (after a couple of hours) then place in the fridge, still in its tin, to thoroughly chill. At least 6-8 hours or overnight.
Remove the cheesecake from the springform tin and serve.