Following this recipe requires a sugar thermometer.
Set the sugar and glucose to cook in a thick-bottomed saucepan until it reaches 145 degrees C on the sugar thermometer. Add the butter and let it melt. Add all the crème fraîche and stir continuously to stop it from catching. Bring the mixture back up to 125 degrees C before turning the mixture out into a toffee tray. Leave it to cool and set overnight. The next day cut the sheet of caramel into squares and wrap the finished caramels in cellophane wrappers.