Prepare the Strawberries:

1. In a large bowl, lightly mash the chopped strawberries with a potato masher until they reach a slightly chunky consistency. Ensure that the fruit is evenly prepared for cooking.

Mix Ingredients:

1. Combine the mashed strawberries, granulated sugar, and lemon juice in a heavy-bottomed pot. Stir well to ensure the sugar is evenly distributed.

Bring to a Boil:

1. Place the pot over medium-high heat and bring the mixture to a full rolling boil while stirring continuously. Once boiling, stir in the pectin and return the mixture to a boil.

Cooking Time:

1. Boil the mixture for 1-2 minutes, continuing to stir to avoid scorching. Use a candy thermometer if needed to ensure the temperature reaches 220°F (104°C), which is crucial for setting.

Skim and Jar:

1. Remove any foam from the surface with a spoon, then carefully ladle the hot jam into sterilized jars, leaving a 1/4-inch headspace.

Seal and Process:

1. Wipe the rims clean, apply lids and bands, and process in a boiling water bath for 10 minutes to ensure proper sealing. Adjust processing time based on altitude if necessary.

Cool and Store:

1. Remove the jars and let them cool undisturbed for 12-24 hours. Check the seals and store any unsealed jars in the refrigerator. Properly sealed jars can be stored in a cool, dark place for up to one year.