Tomato Jam

Rinse the tomatoes and cut in half. Remove the cores and coarsely chop. Peel the lemon, and finely dice the pulp. Add the tomatoes, lemon, sugar, salt, and vinegar to a saucepan. Bring to a boil, then reduce the heat to low. Cook for 45 minutes, stirring occasionally. Fill the prepared jars to the brim with the jam and seal tightly. Turn upside down and cool slightly, then turn right side up and cool completely.