Prepare the Strawberries:
Wash the strawberries only when ready to use them. DON'T remove the stem before washing, the strawberries will absorb extra water.
After you washed them under cold water, let them drain in a colander for a few minutes.
Check and discard any mushy or moldy berries.
Cut and discard the stem, and slice the strawberries into quarters or dice them.
Add them to a large enough, heavy bottom saucepan, and mash using a potato masher.
Add sugar, lemon juice, and lemon zest and let them sit for about 20 minutes. The strawberries will release more juice.
Place the saucepan over low-medium heat and stir until the sugar is dissolved. After which increase the heat to medium-high, bring to a rolling boil, decrease the heat to medium and simmer and stir for about 15-20 mins or more if needed, until the mixture is bubbly and thick.
If you prefer the jam to be even thicker, in a cup, mix two tablespoons of cornstarch with 4 tablespoons of water until dissolved and add the mixture to the jam. Stir and simmer for a few minutes. Repeat if needed, but keep in mind, the jam will thicken more as it cools.
Transfer jam to jars and let cool to room temperature, seal and transfer to the refrigerator for up to two weeks or more.
Check the post for tips on freezing the jam.