Combine peaches, raspberries, and lemon juice into a large saucepan
Crus fruit slightly – or a lot as you prefer. I find a potato masher works well for this
Add fruit pectin, and stir to dissolve
Add the butter now if you’re using it. The purpose of the butter is to help keep the jam from developing a foam. It’s not a necessity, but it does help.
Bring fruit mixture to a rolling boil
Add sugar, and stir until dissolved
Bring back to a rolling boil that cannot be stirred down
Set your timer for one minute and continue boiling
When time is up, remove from heat, and using a spoon, skim any foam that may have developed. I skim it into a bowl or jar and keep it in the fridge to use first
Ladle into clean, hot jars to about 1/4 inch from the top