The original recipe doesn't call for it but I also added 1/2 tsp of fresh nutmeg.
Wash and stem mulberries.
Cover mulberries with cold, salted water. Use 1/4c salt to 1 qt water. Let stand 5 minutes. Drain and rinse with fresh water 3 times.
Crush berries. Add sugar, lemon juice and cinnamon (& nutmeg if using). Cook slowly, stirring, until sugar dissolves. Boil rapidly, stirring constantly to prevent scorching, until jelling point is reached (220 degrees, I'm not sure what it is for high alt.) Remove from heat and skim foam. Ladle into hot jars. Seal and process in boiling water bath for 10 minutes.
It's a hassel stemming the barries but it is well worth the work.