Place prickly pears in a large pot and add just enough water to almost cover them.
3 pounds ripe prickly pears
Bring to a boil, then turn off the heat and let steep, covered, for 30 minutes.
Mash the fruit with a potato masher, then press through a food mill to remove seeds.
Strain the pulp through a fine mesh strainer lined with cheesecloth (or a paper towel) to remove every tiny glochid.
Measure the strained juice and return it to the pot. Add an equal volume of sugar.
3 cups granulated sugar
Simmer over medium heat for 5 minutes, then turn off the heat and let cool for 15 minutes.
Stir in lime juice (or citric acid) a little at a time until it reaches your preferred tartness.
4 limes
While still hot, pour into clean Mason jars and seal.