Thoroughly wash the rhubarb to remove any dirt, and ensure no leaves remain, as they are toxic and should be discarded.

Slice the rhubarb into small, even pieces, approximately 1–2 cm in length, for uniform cooking.

In a large saucepan, combine the rhubarb pieces and caster sugar. Allow the mixture to sit at room temperature overnight. This resting time helps the sugar dissolve and draws out the natural juices from the rhubarb.

The next day, place the saucepan over medium heat and cook the mixture, stirring occasionally, until it reaches a rolling boil. Monitor it closely to prevent sticking or burning.

Once boiling, lower the heat and let the mixture simmer gently for 30–35 minutes, stirring occasionally. The jam should thicken as it cooks.

Add a few drops of fresh lemon juice to enhance the flavor and help the jam set. Stir well and continue cooking for an additional 5 minutes.

To check if the jam is ready, place a small amount on a cold plate. Let it cool slightly, then push it gently with your finger. If the surface wrinkles, the jam has reached the correct consistency.

Remove the saucepan from the heat and let the jam cool for about 15 minutes before transferring it to jars.

Spoon the warm jam into clean, sterilized jars, filling them nearly to the top. Seal the jars tightly with lids. Once cooled completely, store the jars in the refrigerator, where the jam will keep fresh for several months.