First, wash, dry and roughly chop the mint leaves.

Add the leaves and the water to a large saucepan.

Bring to the boil. You can crush the leaves with a potato masher to get more flavor if you wish.

Turn off the heat and let stand for at least 10 minutes. If you want a stronger mint flavor, let it stand for up to 30 minutes.
Strain the leaves out, measuring 3 cups of the liquid as you do.

Add the 3 cups of liquid back into the saucepan with the lemon juice. Add the butter, if using.

Whisk in the pectin and bring the mixture back to the boil.

Slowly add in the sugar, whisking as you go, making sure the sugar is being stirred through and dissolves. Once the mixture reaches a rapid boil, cook for an additional 2 minutes before pouring into sterilized jars.

If canning, make sure to follow proper canning instructions for processing - usually 10 minutes in a water bath.

NOTE:

The butter is not necessary, but it does help dissipate the foam that collects on top of jams and jellies. If you don't use it, that's okay, you can skim the top of the jams and jellies to remove and discard any foaming that occurs. I discovered that unrefined coconut oil can be substituted for the butter for lactose intolerance.