1. Put a small porcelain plate in the freezer.

2. Combine the strawberries, sugar, salt, and lemon juice in a large pot and cook it over low heat for about 30 to 40 minutes. The mixture should always be simmering, but not boiling or bubbling and spurting liquid. Test the doneness of the jam by dripping a little but on the cooled plate and tipping it. If it runs quickly it needs to be cooked more. If it runs slowly it is done. You may need to test it a few times before it is done.

3. Remove the jam from the heat and stir in the butter until it melts. Then, scoop the mixture into a sterilized pint jars. Process for 20 minutes in a hot water bath if you would like to seal them.

4. Allow the jars to cool to room temperature. The jam will set as it seals.