Start by preparing your jam jars. You can do this in your dishwasher using the sterilize cycle or you can simmer the jars and lids in water on the stovetop for 15 minutes.

Place 2 or 3 small plates in the freezer. You will use these later to test the gel point of the jam.

Heat a large (6-quart) stockpot over low heat. Add the strawberries and lemon juice. Stir in the pectin until dissolved. Bring the mixture to a boil – a boil that is vigorous enough that it continues to boil even when stirred.

Add the sugar all at once. The mixture may bubble up, but it will settle and the sugar will dissolve. Swirl the pot to dissolve the sugar but do not stir with a spoon. Turn up the heat and bring everything back to a strong boil. Once it is at a strong boil, continue to boil vigorously for 1 minute.

Turn off the heat and skim away any foam that rises to the surface.

Test to see if the jam has set by dropping a teaspoon of jam on one of the plates that have been in the freezer. If the jam has reached its gel point and you have added enough pectin, the jam will set up quickly on the plate. If it is a good consistency, proceed to the next step. If the jam is too runny, simply continue to boil it, checking every 5 minutes with a new plate.

Using a wide funnel, fill the sterilized jars with hot jam, leaving ¼-inch of room at the top. Wipe any jam from the top and sides of the jars with a clean towel. Screw on the lids, but do not over-tighten.

Preserve the jam for long storage by using the water bath canning method (see remaining instructions), or simply refrigerate the jars and eat within a few weeks.

If you want to use the water bath caning method, bring a large 8- to 10-quart stockpot full of water to a rolling boil. Place a rack in the bottom of the stockpot.

Submerge the filled jam jars in the simmering water and bring the water back to a boil for 15 minutes. Turn off the heat and let the jars stand in the water for 5 minutes.

Remove the jars from the stockpot using tongs or a jar lifter. Check to see if the lids are tightly sealed. As the jam cools, the lids should pop inward – you might hear this as they cool. Store jams with inverted lids at room temperature until you open them. If the lids of any jars did not invert and are popped upward, store in the refrigerator and consume within a few weeks.