First place a small plate in the freezer ( this is to check the Marmalade is set later)
Place the Sliced Tangerines in a large saucepan, add the 600ml of water, simmer for 20 minutes until the tangerine rind softens.
Add the sugar and stir in until completely dissolved.
Add the lemon juice and Cinnamon. Boil for 20-30 minutes. ( Tip- if you like less rind in your marmalade, half way through cooking, pick out some of the rind with a fork)
To test the Marmalade is ready. Retrieve the plate from the freezer, spoon a small amount on the plate, push the edge of the Marmalade with your finger, if it wrinkles it's ready