Rinse the green tomatoes and pat dry. Remove stems, cut into quarters, and scoop out the juice, seeds, and white core.
In a glass or stainless steel bowl, combine the tomato quarters, sugar, and lemon juice. Top with parchment paper to prevent oxidation and macerate for at least 12 hours.
Transfer to a jam pot, add the cinnamon stick, and boil for 10 minutes, stirring occasionally. When tomatoes are tender, remove the stick. Pass through a fine vegetable mill, then return to the pot.
Cook over low heat, stirring constantly, for another 10 minutes. Skim foam carefully. Test for set—it should coat a spoon. Pour into sterilized jars immediately, add cinnamon chips to each, seal, and cover.
Note: As an experienced home preserver, I turn jars upside down after filling and cool them this way for extra sterilization.
