First, make sure your jam jars, lids and rings are clean and sterilized. You can sterilize them in the dishwasher, or by boiling them for a few minutes in a large stock pot.
Wash and pit the cherries, if they're not already pitted. Combine the pitted cherries in a stock pot with the lemon juice, vanilla and bourbon.
Bring the cherries to a simmer over medium heat. Mash the cherries slightly, leaving the fruit as chunky as you'd like.
Sprinkle the pectin over the fruit and stir it in. Increase heat to medium/high and stir constantly (while wearing oven mitts to protect against splatter burns), and bring to a boil.
Dump all the sugar in at once. Continue stirring constantly to return to a vigorous boil that can’t be stirred down. Boil hard while stirring for 1 minute.
Remove from the heat and stir in the butter (the fat helps to reduce any foaminess).
Immediately ladle the jam into hot, sterilized jars, leaving a 1/4 inch gap at the top (called "head space") to allow for expansion. Wipe the rims of the jars with a clean damp cloth. Center the lids on the jars, and screw on the lids "fingertip tight".
Jam stored in the refrigerator should be consumed within 1-2 months.