Sterilise two medium jars (you can use the dishwasher and then allow to air dry if it's still a little wet.)
Wash and dry oranges. You'll need about 2 large or 3 medium oranges.
Chop oranges into quarters and then slice off and discard the middle pith and very ends of the orange quarter. Remove any visible seeds, too.
Thinly slice the quarters until you have 500 grams and then place into a saucepan.
Add vanilla and water.
Bring to the boil. Simmer for 10 minutes, stirring every now and then.
Take off heat, add sugar and stir before returning to heat.
Bring to the boil again and then adjust so the mixture is simmering at a medium pace, not furiously and not gently.
Allow to simmer for about 20-30 minutes, stirring occasionally. You'll know the jam is ready when it loses its watery appearance and starts to look shiny and "grab" the bottom of the saucepan a little as you stir.
Pour into the jars and seal with a lid.
Store marmalade in fridge.