Step 1
Heat lemon juice water sugar lemon zest and cornstarch in a pot over medium heat. Simmer until thickened about 5 minutes; remove from heat.
Step 2
Sterilize the jars and lids in boiling water for at least 5 minutes.
Step 3
Pour the lemon syrup into the hot sterilized jars filling the jars to within 1/4 inch of the top.
Step 4
Run a knife or a thin spatula around the insides of the jars after they have been filled to remove any air bubbles.
Step 5
Wipe the rims of the jars with a moist paper towel to remove any food residue. Top with lids and screw on rings.
Step 6
Process jars in boiling water in a large pot for 10 minutes; remove jars from pot and allow to cool.
Step 7
Once cool press the top of each lid with a finger ensuring that the seal is tight.