Wash the tomatoes, cut into small cubes. Wash the orange, dry it, trim the zest, and chop it into strips. Cut the orange pulp into medium-sized pieces.
Place the chopped tomatoes in a large saucepan, pour in 1 cup of water, and place the saucepan over low heat. Close the lid and cook until the juice appears and the tomatoes soften.
Add sugar to the saucepan and cook until the sugar dissolves. Add zest and chopped orange. Cook over low heat for 35-40 minutes. Transfer to sterilized jars, cover with lids and let cool at room temperature. Store in the cellar or refrigerator.
Serve the jam with porridge, cheesecakes, baked goods or casseroles.