Ingredients

450g Seville oranges
225g Blood oranges
Juice of half a lemon
1.75 litres water
1.4kg granulated, cane sugar

1.  Weigh the preserving pan un lidded and record the weight. Juice the oranges and lemon. Pour the juice with the water into the pan. Remove the inner membranes ( not the pith) and pips from the fruit with a small sharp knife.

2. Put the membranes from the oranges into a processor or mini-chopper and chop finely. Place these and any pips into a 36 cm x 36cm piece of thin cotton muslin. Tie this up with string and add it to the pan. Shred the peel and add it to the pan.  If possible, leave the pan overnight to allow the fruit to soak. 

3. Next day, bring the lidded pan to boil, turn down the heat and simmer very gently for two hours.  Warm the sugar in a low oven, 120C for 20 minutes.

4. Remove the lid from the pan and set aside. Lift up the muslin bag and squeeze the liquid from the bag back into the pan through a sieve, using a large spoon.  Weigh the pan on a flat set of scales, protected with a trivet or heat resistant mat. Look for a weight of the empty pan( see point 1 ) plus 1.4kg. If the weight is more, return the un lidded pan to the heat and simmer gently, checking the weight every 5 minutes until the desired weight is reached. Warm the sugar in an oven 120C for 20 minutes 

5. Add the sugar to the pan and stir until dissolved. Put clean jars in the oven to warm through. Gradually bring the pan to a rolling boil and test for a set after 8 minutes, using the flake test. As soon as setting point is reached, turn off the heat

6  Leave the marmalade to cool for 10 minutes, a skin should have formed on the surface. Remove any scum from the surface  with a large metal spoon. Gently stir the marmalade to distribute the peel.

7. Pour the marmalade into clean, warm sterilised jars, cover and seal  with new twist top lids. Leave the jars upright and undisturbed to set.