In a medium-large saucepan, combine the cream, milk, caster and brown sugars, butter, glucose, salt, and 30ml of water. Place over a medium-high heat and cook, whisking constantly, until the mixture reaches 119 C, measured with a sugar thermometer. This will take about 25-30 minutes.
Remove from the heat and pour into the loaf pan. Sprinkle sparingly with the extra sea salt and leave to cool completely at room temperature.
Cut into small squares; can be wrapped individually with wax paper.
Notes
Store in an airtight container for up to 10 days.
Use a much larger saucepan than you think you’d need, as the mixture will bubble up to twice the size whilst cooking.
Be careful the temperature doesn’t exceed 119 C or the caramel will be too hard and chewy, but don’t stop too early or the caramel will be soft and pale.
