Prep canning equipment. Wash the jars with hot soapy water. Place the jars in the water bath canner with enough water that you can fully submerge the jars. Set the burner to medium and allow the jars to simmer in hot water. Place the lids and rings in a simmering pot of water. Place over medium heat covered.
Prep peels and simmer. Cut the top and bottom off of the oranges and lemons. Using a vegetable peeler, peel the colorful parts off the oranges and lemons. Cut the peels into thin slices and set aside. In a 6-8 qt pot add the water and baking soda. Place the peels in the large pot over medium heat and allow to simmer covered for 20 minutes.
Add fruit to the pot. Remove the membrane (the pith) from the oranges and lemons. Chop the fruit into pieces. You should have about 4 cups of fruit and juice. For larger oranges or lemons you’ll want to reduce the amount of fruit so you get a total of 4 cups of chopped fruit and juice. Transfer the cut fruit and juice to the pot with the peels. Cover and allow to simmer for 10 minutes.
Add pectin and boil. Add the pectin and stir the mixture until the pectin is well combined. If you’re using butter, add it now. This will reduce foaming that happens during the boiling process. Bring the mixture to a full rolling boil over medium-high heat. Allow to boil for 2 minutes stirring constantly. *A full rolling boil means that the mixture is fully boiling while you’re stirring.
Add sugar. Add the sugar all at once and stir to combine. Bring the mixture back up to a full rolling boil and allow to boil for 1 minute.
Skim foam. Remove from the heat, and skim any foam off the top using a metal spoon.
Fill jars. Ladle the hot jam into the hot jars. Fill the jars with a ¼ inch of headspace.
Wipe rims and top jars. Wipe the jar rims with a moist paper towel. (it can be water or white vinegar). Place the jar lid on top followed by a ring. Tighten the rings to the fingertip tight.
Process. Transfer jars to a prepared water bath canner. Bring to a boil and once the water is boiling set the timer for 10 minutes. Process for 10 minutes, adjusting for altitude.Turn off the heat, remove the lid from the water bath canner, and allow the jars to sit for 5 minutes before removing them.
Cool and check seals. Transfer jars to a heat-safe space and allow to cool for 12-24 hours. Check the lids for a proper seal by pressing on the center. The center shouldn’t pop up. Store in a cool place for up to 18 months.