Here's the recipe I'm going to use:
2 2/3 cups crushed pitted peeled peaches
1 1/3 cups crushed blackberries
3 tablespoons fresh lemon juice
7 1/3 cups sugar
1/2 teaspoon butter (optional)
1 pouch (3 ounces) liquid pectin
Prepare canning jars and lids. Bring water in a bath canner to a boil.
In an 8-quart stainless steel stockpot, combine peaches, blackberries and lemon juice. Gradually stir in sugar and butter, if using. Bring to a boil over medium heat, stirring constantly until sugar is completely dissolved.
Increase heat to medium-high. Bring to a full boil, stirring constantly. Stir in pectin. Return to a full boil, stirring constantly. Boil 1 minute.
Remove from heat. Skim any foam that rises to the surface. Let jam cool in pot 5 minutes, stirring occasionally.
Ladle hot jam into hot jars, leaving 1/4-inch headspace. Remove any air bubbles. Wipe jarm rims and thread with a clean damp paper towel. Center hot lids on jars. Screw on bands.
Place jars in canner, making sure they are covered by 1 inch of water. Cover canner. Bring to a boil. Preocess 10 minutes.
Remove jars from canner. Place on a wire rack or cloth towel. Let cool 24 hours. Wash and dry jars and store in a cool dark place.From Dispatch Kitchen