Martha's Strawberry Jam

In a glass bowl, stir together berries, sugar, and lemon juice. Refrigerate overnight. Transfer to a large, heavy pot and bring to a simmer, stirring until sugar has dissolved. Return to bowl, cover, and refrigerate overnight. Strain syrup into a large, heavy stockpot; reserve berries. Bring syrup to a boil, then cook until a thermometer registers 221 degrees. Add berries; boil 5 minutes more, skimming foam as needed. Pour into hot sterilized jelly jars. Let cool completely, cover, and refrigerate up to 2 weeks, or freeze up to 6 months.