Prepare boiling water canner. Heat jars and lids in simmering water until ready for use. Do not boil. Set bands aside.
Combine strawberries and lemon juice in a 6 to 8-quart saucepan. Gradually stir in pectin. Bring mixture to a full rolling boil that cannot be stirred down, over high heat, stirring constantly.
Add entire measure of sugar, stirring to dissolve. Return mixture to a full rolling boil. Boil hard 1 minute, stirring constantly. Remove from heat. Skim foam if necessary.
Ladle hot jam into hot jars leaving 1/4 inch headspace. Wipe rims. Center lid on jar. Apply band until fit is fingertip tight.
Process in a boiling water canner for 10 minutes, adjusting for altitude. Remove jars and cool. Check lids for seal after 24 hours. Lid should not flex up and down when center is pressed.
STRAWBERRY VANILLA JAM: Add half a vanilla bean, split in half lengthwise, to the crushed strawberries. Cook as directed and remove vanilla bean before ladling jam into jars. The resulting jam will be enhanced with subtle yet distinct vanilla overtones.
STRAWBERRY BALASMIC JAM: Reduce the lemon juice to 1 tbsp and add 3 tbsp good-quality balsamic vinegar. Balsamic vinegar accents the strawberry flavor and gives the jam a robust taste.
STRAWBERRY LEMON JAM: Add the grated zest of 1 large lemon to the crushed strawberries.
PEPPERED STRAWBERRY JAM: Stir 1/2 tsp freshly ground black pepper into the cooked jam just before ladling it into the jars. Pepper accents and compliments strawberries' sweet flavor. Be sure to use freshly ground pepper, which delivers a fresher-quality flavor.