Wash and dry the strawberries, and dice it into ½ inches pieces. Dice it about eight full cups.
Peel and chop the kiwi into ½ inch cube pieces.
Add cubed kiwi and strawberries to a large bowl.
Stir the fruits along with sugar, lemon juice, and lemon zest.
Add chopped mint and vanilla extract.
Cover and leave it to macerate for about two hours. You can also refrigerate overnight.
The next step is to sterilize the jars. With boiling water, clean the jam jars with a kitchen towel.
In a large, heavy pot, add the fruit mixtures.
Cook on medium-high heat and carefully stir the mixture.
Stir the mixture often as it comes to boil and stir relentlessly when it reaches a hard boil.
After 25-30 minutes, the jam will be thick and add butter to break up the foam.
Using a spoon, scoop up the remaining foam and turn of the heat.
Carefully spoon the hot preserves in the warm jars leaving about ½ inch headspace.
To remove any air bubbles, run a plastic knife around the jar.
Wipe jar rims with a damp towel and seal it.
Boil the jars for 10 minutes and let them cool for 12 hours.
Test the jar seal by removing rings and lifting them with their flat lids.
You can store it for 3-4 months.