• Wash and carefully peel the prickly pears while wearing gloves to avoid the tiny glochids (spines).
• Roughly chop the peeled fruit and place it in a large saucepan with just enough water to cover fruit and prevent sticking.
• Simmer over medium heat for 15–20 minutes, stirring occasionally and gently mashing the fruit until softened and juicy.
• Strain through a jelly bag or several layers of cheesecloth until you have clear juice. Measure exactly 2 cups of juice.
• In a large saucepan, combine the prickly pear juice, bottled lemon juice, and sugar.
• Bring the mixture to a full rolling boil over high heat, stirring frequently. A rolling boil should continue bubbling even while stirring.
• Stir in the liquid Certo and return the mixture to a full rolling boil.
• Boil hard for exactly 1 minute, stirring constantly.
• 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).
• Remove jars and allow them to cool undisturbed for 12–24 hours before checking for a set.

Notes

• Bottled lemon juice is recommended for consistent acidity.
• Avoid squeezing the cheesecloth or jelly bag too firmly, as this can make the jelly cloudy.
• Jelly may take up to 24 hours (occasionally longer) to fully set.
• Store unopened jars in a cool, dark place. Refrigerate after opening.