Remove the tip of the stalk from the oranges and place the whole oranges and lemon juice in a large preserving pan or large cooking pan. Cover the fruit with four pints of cold water. Bring to the boil, cover and simmer gently for two hours. The skin will be extremely soft and easily pierced with a fork.
Now add the vanilla pods. Cut the pods in half, split the pod and scrape the vanilla seeds into the pan, also adding the vanilla stick. Leave for a few hours to cool down and infuse the vanilla flavours (or overnight).
Remove the oranges from the pan, retaining the water and vanilla sticks in the pan. Cut all the oranges in half and scoop out the pips and pith, adding back into the reserved water.
Warm 1.6kg of granulated sugar on a baking tray in the oven on a low heat for 15 mins.
Bring the pan of retained water with the pith and pips to the boil for 6 mins.
The white part of the rind, including the pith, is a source of pectin and has nearly the same amount of vitamin C as the flesh and other nutrients.
At this stage, shred the peel. Rather than using a sharp knife to do this, use a pizza cutting wheel. The pizza cutter creates lovely fine shreds and is safe for children to help out too.
Shred the peel into lovely slender pieces. After the pulp and pith has boiled for 6 mins, strain through a colander, retaining the warm water and adding back into the preserving pan. Add the warmed sugar with the shredded peel into the pan. The preserving pulp and pith can now be squeezed through a piece of muslin removing as much of the juice as possible. This will give the marmalade a lovely set.
Now add the 1kg of pectin jam sugar, stirring over a warm heat until all the sugar has dissolved, around 10 mins. Now bring to the boil and bubble rapidly on a rolling boil for 25 mins, to reach setting point.
Take the pan off the heat and remove any scum from the surface with a wide spoon (or to dissolve any scum place a knob of butter on the surface). Leave the marmalade to cool in the pan for 30 mins and the peel to settle. For a guaranteed firm set marmalade add 250ml Certo Apple Pectin Extract at this stage as the marmalade cools.
Pot the marmalade into sterilised jars, seal and label. If you would like an extra vanilla flavour, add half a stick of vanilla into the marmalade before sealing the jar.
Leave the jars of Vanilla Marmalade to set for 24 hours.