Fill your water bath canner with enough water to cover the jars by at least one inch and begin heating it over medium-high heat. Place clean jars in the simmering water to keep them hot until ready to fill.

Clean and slice all strawberries, then place them in a large, heavy-bottomed saucepan. Add lemon juice and butter to reduce foaming, then gradually stir in the pectin. Bring the mixture to a full rolling boil over medium-high heat, stirring frequently and mashing the strawberries to your desired consistency.

Once boiling, add the sugar all at once and stir until completely dissolved. Return the mixture to a hard, rolling boil and cook for 1 to 2 minutes, stirring constantly to prevent sticking. Remove from heat and skim off any foam if necessary.

Ladle the hot jam into hot, sterilized jars, leaving ¼ inch headspace at the top. Wipe the rims clean with a damp cloth to ensure a good seal. Center the lids on the jars and screw on the bands until fingertip-tight.

Carefully place the filled jars into the boiling water canner. Ensure the water covers the jars by at least one inch. Once the water returns to a full boil, start your processing time, process for 10 minutes (adjusting for altitude if needed).

When finished, turn off the heat and let the jars rest in the canner for 5 minutes before removing. Place the jars on a towel-lined counter and let them cool undisturbed for 12 to 24 hours. Check the seals once cool—the center of each lid should be concave and not flex when pressed. Label, date, and store your jam in a cool, dark place.

This recipe yields about 4 pint jars or 8 half-pint jars of delicious homemade strawberry jam.