In a large stockpot, cover corn cobs with water. Add lid to pot to keep moisture in. Boil cobs for just under an hour. Remove from heat.
Measure out 4 C of liquid, strain if desired.
Return the liquid to the pot, add pectin and lemon juice and stir to combine.
Bring to a boil. Add granulated sugar.
Bring to a second boil - this time, the boil cannot easily be stirred down. Add 1 tsp butter to reduce foaming (optional).
Once the jelly reaches a temp of 220 degrees F, boil hard for allotted time (1-2). One minute for a softer set, two minutes for a harder set.
Fill half pint jars, allow 1/2" of headspace.
Wipe rims of jars, then place lids and rings. Tighten.
Process for 10 minutes in water bath canner. This recipe will make 5 half pint jars.