Classic Strawberry Jam

Yield: 8 cups

2 quarts strawberries, washed, stems removed, cut and crushed to yield 5 cups crushed berries (see notes)
7 cups sugar
½ teaspoon butter (reduced foaming)
1 (1.75oz) box fruit pectin (I use Sure-Jell)

Pour the crushed strawberries with all the juices into a large pot. Measure the sugar into a separate bowl and set aside. Stir the package of pectin into the strawberries and add the butter.
Stirring frequently, bring the strawberry mixture to a full rolling boil (a boil that does not stop bubbling when stirred), and then add the sugar. Stir to fully incorporate.
Return the mixture to a full, rolling boil and boil for exactly 1 minute, stirring constantly.
Remove the pot from the heat.
Skim any foam from the surface.
Ladle quickly into clean jars. (I like to use a wide funnel.)
Wipe the rims of the jars with a clean cloth.
Place the lids on the jars and tighten the bands to "fingertip tight," meaning snug but not too tight.
Place the jars in a canner and process (gently boil) for 10 minutes. The water should cover the jars by an inch or two – add additional boiling water, if necessary. Carefully remove the jars from the canner. (No canning pot? See main post for convenient alternative.)
Cool completely before storing. Make certain all lids have sealed properly before storing: If the lid springs back when pressed in the middle, it is not sealed and should be stored in the refrigerator.

Frozen strawberries work beautifully. Once they are partially thawed, I chop them. (They are easy to chop when still somewhat frozen. When fully thawed, you will lose a good bit of the juice, and you want that in your jam.) Then I place them in the pot and mash once they are thawed enough to easily do so.
More recently with fresh berries, I roughly chop them and then crush the berries by squeezing with a clean hand. My hand gets a little red, but it's an efficient way to thoroughly crush them. You can also do this with frozen berries once they have fully thawed.