Remove any greens from the strawberries and cut into fourths.
In a medium to large pot, combine the strawberries, sugars, lemon juice and zest. Cook over medium heat until the sugars are liquid and the strawberries have softened (3-5 minutes).
Use an immersion blender to puree the mixture. I like my strawberry jam pretty smooth, but you can also leave the texture more chunky if you prefer.
Continue to cook on medium/high heat for another 10 minutes. The mixture should be at a low boil. It should reach between 210°F and 220°F. Keep an eye on it and continue to stir so it doesn’t burn the bottom of your pan.
Remove from heat and allow to cool. It will thicken as it cools. Store in an airtight container in the refrigerator for at least 2 weeks.
Notes
I use the zest from the entire lemon but juice from only half the lemon. Put the rest of the lemon in your water or use for something else. If you don't have an immersion blender, you could also add the mixture to a blender or food processor and puree, then return to the pot. I like the mixture of granulated white and brown sugar as it adds just a little depth and flavor without taking away from the strawberry flavor. But if you want or need to use all granulated white sugar you can.Swap out the lemon for another citrus if you like—such as lime or orange.