Step 1: Prepare the Oranges

1. Wash and cut the oranges: Thoroughly wash the oranges, then cut them in half. Squeeze out the juice and reserve the juice for later.
2. Remove the pith and slice the peel: Using a spoon or knife, remove as much of the white pith as possible from the orange halves. Slice the peel into thin strips based on your preference for chunky or fine marmalade.

Step 2: Cook the Oranges

1. Add water and orange peel: Place the sliced orange peel, lemon juice, and reserved orange juice into a large, heavy-bottomed pot.
2. Simmer the mixture: Pour in the 2.5 liters of water and bring the mixture to a boil. Lower the heat and let it simmer for 2 hours, or until the peel becomes soft and tender.

Step 3: Add Sugar and Boil

1. Add the sugar: Stir in the granulated sugar and keep stirring until it has completely dissolved.
2. Boil the mixture: Increase the heat and bring the mixture to a rapid boil. Continue to boil for 15-20 minutes, stirring occasionally, until the marmalade reaches its setting point (test by placing a small spoonful of marmalade on a chilled plate—if it wrinkles when pushed, it’s ready).

Step 4: Jar the Marmalade

1. Sterilize the jars: While the marmalade is boiling, sterilize your jars by washing them in hot, soapy water and placing them in a low oven (100°C/210°F) for 15 minutes, or you can boil them in water for 10 minutes.
2. Fill the jars: Once the marmalade is ready, carefully pour it into the sterilized jars, leaving a little space at the top. Seal with sterilized lids while still hot.

Step 5: Let the Marmalade Set

1. Cool and store: Allow the jars to cool completely, then store in a cool, dark place. The marmalade will be kept unopened for up to a year. Once opened, store in the fridge.