Wash and hull the strawberries. Slice them into halves or quarters, depending on their size. Finely grate the lemon zest (if using).

In a large saucepan, combine the strawberries, sugar, lemon juice, and lemon zest. Gently stir to combine.

Let the mixture stand for at least 30 minutes, or up to an hour, to allow the strawberries to release their juices and the sugar to dissolve partially. Stir occasionally.

Bring the mixture to a rolling boil over medium-high heat, stirring frequently to prevent sticking. Once boiling, reduce the heat to medium-low.

Boil gently, stirring occasionally, until the jam reaches the setting point (approximately 220°F/104°C on a jam thermometer, or wrinkles when tested on a chilled plate).

Remove from heat. If canning, carefully ladle the hot jam into sterilized jars, leaving about 1/4 inch of headspace. Wipe rims clean, seal, and process according to your preferred canning method.

If not canning, let the jam cool completely in the saucepan before transferring it to sterilized jars or containers. Store in the refrigerator for up to 3 weeks.