Melt the butter in a microwave or a small saucepan
Crush the biscuits into even crumbs using a rolling pin and a bag, in a bowl or a food processor
Mix the pulverised biscuit crumbs and the melted butter.
If you are using 1 x 20cm tin, line the base to assist in removing the completed cheesecake later
Now press them into the base of the tin or the ramekins, pressing down firmly. If you don't do this, the base won't stick together and will just crumbs.
Cheesecake
Mix all the filling ingredients together and make sure the sugar has dissolved. Unless of course you would like little molten islands of muscovado in the mix, which would be delicious
Put some greaseproof, clingfilm or waxed paper round the sides of the tin to help you remove the cheesecake from the tin later on. If you are using ramekins, they are fine just as they are.
Pile the cheese mixture into the tin or divide between ramekins, on top of the biscuits, smooth over and leave in the fridge to set. It won’t set hard, but it will firm up enough so you can slice it after a couple of hours.
Topping
Meanwhile, empty the tin of condensed milk caramel into a saucepan and heat gently until runny. Don’t boil it. Stir in half a teaspoon of ordinary salt and stir well to distribute.
Drizzle the warmed caramel over the top of the cheesecake(s) until it is as thick as you like it, you may not need it all, and pop back in the fridge to firm up.
When you are ready to serve, remove the tin from the fridge and pop up the base. Remove the lining paper from the sides and put the cheesecake on a small plate.