2 pounds Seville oranges
5 cups granulated sugar
3 1/2 cups packed dark brown sugar
Juice of 1 large lemon
Wash the oranges thoroughly, then remove the knobby bits from the ends and cut each in half. Thoroughly juice the oranges (I use an electric juicer). Discard the seeds and pour the juice into a large bowl. Cut the juiced halved oranges in half again and r
Put the quarters into a food processor and process until finely chopped (you might need to do this in two batches), or cut the peel into shreds by hand. Add the chopped flesh, peel, and pith to juice in bowl, pour in 2½ quarts (2.5 liters) of cold water.
Stir, cover, and leave to macerate overnight.
The next day, transfer everything into a large pan and bring to a boil (this will take about 15 minutes). Once at boiling point, reduce the heat and simmer for another 1½ hours, or until the peel is soft.
Add the sugars and lemon juice and stir over the heat until the sugar has dissolved.
Increase the heat to bring the liquid to a rolling boil. Do not stir the marmalade from this point on. After 20 minutes, test to see if it has reached setting point. If it hasn’t, leave for another few minutes, then test again.
Remove the pan from the heat, leave to stand for 10 minutes, then ladle the marmalade, or pour it from a pitcher, into sterilized jars and seal.