Although it's always best to use fresh berries when possible, wonderful jam can easily be made from frozen strawberries as well. Defrosting the strawberries beforehand will speed the process along. You can use them straight from the freezer, but it will take a little longer to reach jam stage.
Place strawberries, lemon juice, sugar and pectin in the pot. For every quart of frozen berries, use 1/8th cup of lemon juice and about 4 cups of sugar. Stir together; if berries are frozen, you may have to wait until they defrost.
Turn burner up to the highest level of heat that it can reach. Continue stirring.
Watch your jam as the strawberries start to turn to mush and the mixture begins to come together. Add the pectin. Use the amount recommended on the package for the amount of berries you've cooked. Stir occasionally; stirring continuously is not necessary. Make sure you stay close enough to your pot to observe.
Bring jam to a rolling boil and cook for one full minute. Add a pat or two of butter and stir into jam. Turn the heat off.
Funnel jam into prepared home canning jars and can in your usual manner.