If using fresh strawberries wash, cut stems, hull cores, cube, or mash down with a potato hand masher tool or something similar before/during cooking. This makes it easy to reduce down.
If using frozen whole berries (no juice, no stems) just defrost to room temperature, drain excess water, and cut/mash before the reduction process.
In a large saucepan combine fruit, sugar, and lemon juice. Cook over medium heat until almost boiling. Continue mashing and stirring for a few minutes.
Separately mix cornstarch with water until the cornstarch is completely dissolved. Add to the pot of strawberries, stirring constantly until light boiling, water is burned off, and thickened like a loose jam. Takes a few minutes. (if needed turn the heat low, stirring a few extra minutes to cook off loose liquid)
Turn off the heat and let it sit while it continues to thicken more. Completely cool before using-cannot be warm at all-room temperature or chilled.
Shelf Life Store in an air tight container after completely cooled. Stays fresh in the frig for 5-7 days and 3 months in the freezer.Once thawed do not re-freeze.