Prep jars. Prepare jars for canning by washing them with hot, soapy water. Rinse and transfer them to a waterbath canner. Fill the canner until the jars are fully submerged in water. Place them over medium-low heat, cover, and allow them to simmer. Wash your lids and rings, place them on a towel, and set aside.
Cook cranberries. In a saucepan, add the cranberries and water. Place over medium heat and bring to a boil. Once boiling, reduce heat to low and allow to simmer for 5 minutes.
Cool. Remove from heat and allow to cool for 5 minutes.
Process and strain. Working in batches, process the mixture through a food processor, making sure it is nice and smooth. Then, strain the mixture through a fine mesh strainer.
Add sugar and pectin. Transfer the cranberry mixture to the saucepan. Add the sugar and pectin (if using; see notes for why), and bring to a boil over medium heat. Stir constantly to dissolve the sugar completely.
Boil to gel. Increase the heat to medium-high and bring the mixture to a hard rolling boil, stirring constantly. Bring the mixture to the gel stage or 220 degrees F. You can track that using a candy thermometer. If you do not have one, place a plate in the freezer for 5 minutes. Remove the plate from the freezer and drop a teaspoon of the mixture onto the plate. It is ready if you can drag your finger through without the mixture running. If the mixture runs, boil for a few more minutes and test until the mixture does not run. Once it hits the gel stage, remove it from the heat.
Fill jars. Transfer the jars from the waterbath canner and place the canning funnel over a jar. Ladle the hot liquid into the hot jars, leaving ¼ inch headspace. Repeat this process for all 4 half-pint jars.
Debubble and wipe rims. Using your debubbler, remove any bubbles. Using a clean, damp towel, wipe the rims.
Process. Add the lids and rings, tightening them until they are fingertip-tight. Transfer them into a waterbath canner. Fully submerge the jars in water with 2-3 inches above the jars. Cover and bring the water to a boil. Once the water hits a full rolling boil, set the timer for 15 minutes.
Cool. Once the timer goes off, remove from heat, remove the lid, and allow the jars to cool for 5 minutes. Remove the jars from the canner, place them in a heat-safe area, and allow them to cool for 12-24 hours.
Check seals. After 24 hours, confirm a proper seal has been made by checking the centers to see if the center pops up. If it does not, place the jar in the fridge and use it within 5 days. Once a proper seal has been confirmed, remove the rings and store them in a cool, dark place for 12-18 months or per your lid manufacturer’s recommendations.