Simple Strawberry Jam

From Recipezaar.

40 min | 15 min prep

6 pint jars (approximately)

* 3 lbs fresh strawberries, washed and hulled (about 9 cups)
* 4 cups sugar
* 1/3 cup lemon juice
* 1 tablespoon unsalted butter (optional)

* In a large saucepan, bring strawberries up to a simmer over medium-low heat, mashing roughly with a potato masher or flat spoon. Add sugar and lemon juice, stir, and bring up to a simmer for 2 minutes. Add butter and bring to a vigorous boil, stirring often and cook for 10 to 20 minutes, periodically measuring the viscosity of the jam by dabbing a spoonful onto a plate and tipping the plate. Once the jam slows its drip down the plate (it should no longer run like a syrup), remove from heat and skim off foam.
* Fill jars that have been washed, rinsed, dried and boiled in a pot of water for 3 minutes to ¼ -inch from the top. Fasten lids securely and boil jars in a vat of water (be sure jars are completely submerged) for 15 minutes. Remove jars with tongs and let cool upright. Check for secure seals on jars (lid should not spring when touched) and store in a cool place away from light for up to a year.
* Any jars that do not achieve a proper seal should be refrigerated.