"The best thing about this recipe is that it requires no testing for set and works every time. It also tastes fantastic. Better than Seville oranges in my opinion."
Slice grapefruit thinly and add water. Soak overnight.
Measure quantity so you know how much sugar to add. Place in a pot and bring to the boil. Boil for 5 minutes.
Add sugar and stir to dissolve. Bring to the boil and boil rapidly for 5 minutes.
Place the pot in cold water and "figure 8" it with a wooden spoon. The marmalade will thicken and become glossy as the it cools.
When thick and still hot pour it into sterilized jars. You will need approx. 4 x 300 ml jars for 2 grapefruit.