In an 8-quart pot, combine 3 cups pitted, peeled and crushed ripe plums, 5 cups sugar, 1 tablespoons strained fresh lemon juice, and 1/2 teaspoon unsalted butter.
Over medium-low heat, heat the mixture sitting constantly, until the sugar is completely dissolved. Stir in 1/2 cup toasted chopped almonds (can use pecans or walnuts). Increase the heat to medium-high and bring to a full rolling boil, stirring constantly. Stir in the entire contents of the pectin pouch. Boil, stirring constantly, 1 minute. Remove the pan form the heat. Skim off any foam. Add 1/3 cup light rum and stir. Be careful, this will bubble and pop because of the very hot mixture and alcohol.
To prevent floating fruit let the conserve cool for 5 minutes before filling jars. Gently stir the conserve to distribute fruit. Ladle into hot jars, leaving 1/4-inch headspace. Wipe the jar rims and threads with a clean damp cloth; cover with hot lids and apply screw rings. Process 1/2-pint jars for 10 minutes in a 200 degree F water bath, pint jars 15 minutes.