Prep jars. Wash jars, lids, and rings in hot soapy water. Place jars in water bath canner, cover with water, and bring to a simmer.
Cook fruit, lemon juice, and pectin. Combine chopped cherries, lemon juice, and powdered pectin in a large pot. Heat over medium heat, stirring constantly, until mixture reaches a rolling boil. Boil for 1 minute, stirring constantly.
Add sugar and stir.. Add sugar and optional butter, stir to combine. Return to a rolling boil and boil for 3 minutes, stirring constantly to prevent boiling over.
Fill jars. Remove from heat. Ladle hot jam into hot jars, leaving 1/4 inch headspace. Remove air bubbles and wipe jar rims clean.
Process. Place lids and rings on jars, tightening to fingertip tight. Process in boiling water bath for 10 minutes, ensuring jars are covered by 1 inch of water.
Cool and store. Remove from canner and cool for 12-24 hours. Check seals before storing in a cool, dark place for 12-18 months.