In a large kettle, combine cherries and raspberries; stir in sugar. Bring to a full rolling boil, stirring constantly. Add pectin; return to a full rolling boil. Boil 1 minute, stirring constantly. Remove from the heat; skim off foam. Pour hot jam into hot jars, leaving 1/4-in. headspace. Adjust caps. Process for 10 minutes in a boiling-water bath. If, like me, you're using sweet cherries, you may want to cut down on the sugar. My cherry jam turned out delicious, but intensely sweet.
Tip: This homemade jam is a real hit at brunch parties. It makes you seem pretty legit.