2 1/2 cups ground peeled peaches (or very finely chopped)
1 1/2 cups ground pitted plums (or very finely chopped)
3 tablespoons fresh lemon juice
7 1/2 cups granulated sugar
1/2 teaspoon butter, optional
1 pouch liquid fruit pectin
Instructions
Clean the canning jars thoroughly.
Fill a large canning kettle about three-quarters full and bring to a simmer.
Fill a saucepan with water and bring to a simmer; reduce heat to low and add the flat sealing lids. Keep the lids in hot water (do not boil).
In a large, nonreactive pot, combine the finely chopped or ground peaches and plums, the lemon juice, and the sugar.
Cook, stirring, over medium heat until sugar has dissolved. Bring the mixture to a boil that can’t be stirred down. Add the butter, if desired, to keep foaming down. Continue boiling for 1 full minute, stirring constantly. Add the fruit pectin and boil for exactly 1 minute longer, stirring constantly. Remove from heat and skim off excess foam.
Fill a jar with the hot fruit mixture, leaving 1/4 inch headspace. Wipe the jar rims and threads with a dampened cloth and place the seal on top. Screw the lid on firmly but not too tightly. Repeat with the remaining jars until the jam is all used. Lower the jars into the simmering water and add more hot or boiling water to about 2 inches above the jars. Bring to a boil. Cover the kettle and reduce the heat to keep it at a gentle boil. Boil pints or half-pints for 5 minutes.*
Remove the jars to a rack. If a jar does not seal, refrigerate it and use it first. Or, reseal and process again.
Notes
* Higher Altitude Processing Times
For altitudes of 3,001 to 6,000, process for 10 minutes.
For altitudes of 6,001 to 8,000 feet, process for 15 minutes.
For altitudes of 6,001 to 10,000 feet, process for 20 minutes.