In a large saucepan, combine 2 cups of apple juice, 2 tablespoons of lemon juice, and 1 teaspoon of ground cinnamon. Stir well and heat until hot but not boiling, about 5 minutes.

Whisk in 1 package of powdered pectin until fully dissolved. Increase heat to high and bring to a rapid boil, stirring continuously.

Gradually add 1 to 1.5 cups of sugar, stirring until dissolved. Bring back to a vigorous boil for 1 minute.

To check consistency, drop a spoonful of jam onto a chilled plate. If it wrinkles when pushed, it's ready; if not, boil for another minute.

Remove from heat and skim off any foam. Pour hot jam into sterilized jars, leaving 1/4-inch space at the top.

Seal the jars with lids. Process in a boiling water bath for 10 minutes or refrigerate for up to 3 weeks.