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, 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. 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 for 10 minutes. The water should cover the jars by an inch or two. Carefully remove the jars from the canner.

Cool completely before storing. Make sure all lids have sealed properly before storing.