Wash jars and rings with hot water and soap (or in the dishwasher.) Rinse well.
Place jar lids in a sauce pan and cover with boiling water.
Fill a canner half full with water and simmer.
Place sliced, crushed strawberries, measuring five cups, into a 6-ounce or 8-ounce stock pot.
Add pectin to berries, and stir to combine. To reduce foam, add 1 teaspoon butter. Bring to a full boil over high heat, stirring constantly.
Add sugar and stir.
Return to a full, rolling boil and cook for 1 minute, stirring constantly.
Remove from heat and skim off foam.
Ladle into clean, dry jars, leaving 1/4-inch of space at the top. Wipe jars and seal with lids and bands.
Place jars in canning rack and lower into the water, making sure there's 1 to 2 inches of water covering the jars.
Process for 10 minutes and remove jars from canner. Place them upright on a towel.
Once jars are completely cooled, check the seals by pressing the center of each lid. If the lids spring back when touched, they're not properly sealed and they must be refrigerated.