• Wash and prepare the peppers. Remove the stems. Remove the seeds and white ribs from the jalapeños for a milder jelly, or leave some in for extra heat.
• Add the jalapeños, red bell pepper, and apple cider vinegar to a blender. Blend until mostly smooth.
• Pour the pepper mixture into a large saucepan with the strained prickly pear juice.
• Simmer over medium heat for about 10 minutes, stirring occasionally to allow the pepper flavors to infuse the juice.
• Stir in the sugar and bring the mixture to a full rolling boil over high heat, stirring frequently. The mixture should continue boiling even while stirring.
• Add the liquid Certo and stir constantly until the mixture returns to a full rolling boil.
• Boil hard for exactly 1 minute.
• Remove from the heat and skim off any foam if desired.
• Ladle the hot jelly into sterilized half-pint jars, leaving ¼-inch headspace. Wipe the rims, apply lids and bands, and process in a boiling water bath for 10 minutes (adjust for altitude if needed).
• Allow jars to cool undisturbed for 12–24 hours before checking the set.

Notes

• Apple cider vinegar gives this jelly a slightly sweeter, fruitier flavor than white vinegar.
• Adjust the heat by leaving more or fewer jalapeño seeds and membranes.
• Jelly may take up to 24 hours to fully set.
• Store unopened jars in a cool, dark place. Refrigerate after opening.