Peel and finely chop the garlic. Put the tomatoes in a pot. Mix gelling powder and sugar and stir into the tomatoes. Bring everything to a boil over high heat while stirring and boil for at least 3 minutes while stirring continuously.
Season with vinegar, salt and pepper.
Pour jam into hot rinsed twist-off jars. Close, turn upside down and leave on the lid for about 5 minutes. Lasts at least 3 months.