Place a small plate in the freezer before beginning. You will use it later to test whether the apple jelly has reached its setting point.

Prepare two or three clean 250 ml preserving jars. Check that the jars have no cracks or chips and that the lids are clean and undamaged.

Wash the apples and lemon thoroughly under cold running water. The apples will be cooked with their skins, so organic or unwaxed fruit is preferable.

Cut away any bruised or damaged parts. Discard any apple that shows signs of mould or decay.

Cut the apples into quarters or large chunks. Do not peel or core them: the skins, cores and seeds contain much of the natural pectin that helps the jelly set.

Cut the lemon into several pieces. Alternatively, squeeze out its juice and add it to the saucepan with the apples.

Transfer the apples and lemon to a large, heavy-based saucepan. Pour in 300 ml of water.

Cover the pan and bring the liquid gently to a simmer over medium-low heat. Once it begins simmering, reduce the heat.

Cook the apples gently for 45 minutes to 1 hour, stirring occasionally to prevent them from catching on the bottom of the pan.

Check the fruit near the end of cooking. The apples should be extremely soft and should collapse easily when pressed with a wooden spoon.

Line a sieve or colander with a jelly bag, fine muslin or a clean, thin kitchen cloth. Place it securely over a large heatproof bowl.

Carefully transfer the cooked apples and all their liquid into the lined sieve. Leave the juice to drip through for at least 30 minutes.

For the clearest apple jelly, allow the juice to drain naturally without squeezing the cloth. You may press it gently if you prefer a higher yield and do not mind a slightly cloudier result.

Weigh the strained apple juice using kitchen scales. Measure the same weight of granulated sugar. For example, use 650 g of sugar if you collect 650 g of juice.

Pour the juice into a clean, wide saucepan and add the measured sugar. Warm gently, stirring regularly, until all the sugar crystals have completely dissolved.

Increase the heat and bring the mixture to a full rolling boil. Cook for approximately 10 to 20 minutes, stirring regularly and watching carefully because hot jelly can rise quickly.

Skim away any foam that gathers on the surface if you want a particularly clear, polished finish.

Begin testing when the jelly reaches approximately 104–105°C (219–221°F). Keep the thermometer away from the base of the saucepan for an accurate reading.

Remove the chilled plate from the freezer and spoon a small amount of jelly onto it. Wait for 20 to 30 seconds, then push the jelly gently with your fingertip.

The apple jelly is ready when its surface wrinkles slightly and it moves slowly rather than running like water. If it is still too fluid, boil for another two or three minutes and test again.

Remove the pan from the heat as soon as the jelly reaches its setting point. Avoid overcooking, as the jelly will continue to firm up as it cools.

Carefully pour the hot jelly into the prepared jars, preferably using a preserving funnel. Leave the recommended headspace for your jars and wipe the rims clean.

Apply the lids according to the jar manufacturer’s instructions. For shelf-stable storage, process the jars using a current, tested water-bath canning method suitable for the jar size and your altitude.

If you are not following a tested canning process, allow the jars to cool before transferring them to the refrigerator.

Leave the apple jelly undisturbed for 24 to 48 hours before assessing its final consistency. Naturally set jelly may take time to become fully firm.