1. Prepare waterbath preserving pot or stockpot and jars as directed in the Getting Started section.
2. Remove peel from oranges and lemons using a vegetable peeler. Set fruit aside. Thinly slice peel and combine with water and bicarbonate of soda in a medium saucepan. Bring to a boil. Reduce heat; cover and simmer 20 minutes.
3. Remove seeds and any white membrane from oranges and lemons. Finely chop fruit. Add fruit to peel and return to a boil. Reduce heat; cover and simmer 10 minutes. Measure 1 kg (5 cups) prepared fruit.
4. Combine prepared fruit in a large saucepan. Gradually stir in Ball® Jam Setting Mix with Pectin. Add butter, if using. Bring mixture to a full rolling boil that cannot be stirred down, over high heat, stirring constantly.
5. Add entire measure of sugar, stirring to dissolve. Return mixture to a full rolling boil. Boil hard 1 minute, stirring constantly. Remove from heat. Skim foam, if necessary.
6. Ladle hot marmalade into hot jars, one at a time, leaving 0.65 cm (1/4 in) headspace. Wipe rims. Centre lids on jars. Apply bands and adjust to fingertip tight.
7. Process filled jars in boiling water for 10 minutes. Remove pot lid. Wait 5 minutes, then remove jars, cool and store up to 1 year.
Recipe courtesy of Ball