Combine the sugar, lemon zest, and lemon juice in a small saucepan and cook over very low heat for 10 minutes, until the sugar is dissolved.

Add the strawberries and continue to cook over very low heat for 20 minutes, until the strawberries release some of their juices and the mixture boils slowly. Cook until a small amount of the juice gels on a very cold plate. (I keep one in the freezer.)

Pour carefully into 2 pint canning jars and either seal or keep refrigerated. Use immediately, or follow proper canning guidelines.