Wash the oranges and lemons thoroughly. Halve and squeeze out all the juice into your pan. Save every pip and scrap of membrane.

Place all the pips and pithy bits into a muslin cloth and tie securely with string to make a pectin bag.

Slice the peel into strips: 3 to 4mm for thick-cut, 2mm for fine-cut.

Add the sliced peel, juice, muslin bag and 2 litres of water to your pan. Cover with a tea towel and leave overnight at room temperature.

The next day, bring to the boil then reduce to a gentle simmer. Cook uncovered for 1.5 to 2 hours until the peel is completely soft and squashes easily between your fingers. The liquid should reduce by about half.

Remove the muslin bag and squeeze out as much pectin-rich liquid as possible using the back of a wooden spoon.

Add the sugar and stir continuously over a low heat until completely dissolved, about 15 to 20 minutes. Do not boil until every crystal has gone.

Increase the heat and bring to a full rolling boil. Boil vigorously for 15 minutes.

Test for set: place a teaspoon of marmalade on a frozen saucer, wait 30 seconds, then push with your finger. If it wrinkles, it's ready. If not, boil for another 5 minutes and test again. Target temperature is 104 to 105°C on a jam thermometer.

Once set point is reached, turn off the heat and leave to rest in the pan for 10 to 15 minutes. This stops the peel floating to the top of the jars.

Ladle into warm sterilised jars, fill to the top, seal immediately and leave to cool completely. Label with the date.