Process the cookies until fine.
Add the salt and melted butter and mix.
Whip the cream cheese with the sugar until soft and homogeneous. Every once in a while stop and use a spoon to bring down the un-mixed parts that stick on the bowl and at the bottom.
Add the sour cream, vanilla essence and salt and mix again.
Lower the speed of the machine to minimum and add the egg. Mix in at low speed so you don't add any air to them.
Put the muffin liners in the muffin mould. Add a bit of the cookie base and press down with the back of a spoon. Fill with the cheese layer leaving about 3mm free in case it grows a bit. Take to a preheated oven at 180C. Along with the oven, also preheat your oven tray with water so they're cooked in a bain-marie. If you forgot to do this, add boiling water to the tray. The water should go halfway up the side of the muffin mould.
As soon as it goes into the oven, lower the temperature to 150C.
Cook for 15min or until it's barely shaking or not shaking at all if you wiggle the mould gently.
Wait for them to cool down completely and then put in the fridge for at least 2 hours.
Cook everything in a pot until it thickens a bit. Remember that when it cools down it's going to become thicker.
Let cool down completely.