To make tomato jelly, cook ripe tomatoes with sugar and spices in a saucepan until it is reduced to a thick jam. Different spices can be added to create different variations that are sweet or spicy.
Epicurious' tomato jam recipe starts with 2 1/4 pounds of ripe tomatoes. Cut the stem off each tomato, and slice an X in the bottom. Place the tomatoes into a pot of boiling water for about 30 seconds until the skins loosen off the tomatoes. Remove the tomatoes, and pull the skins off. Cut the tomatoes in half, squeeze out their seeds and juice, then cut into chunks.
Place the tomatoes into the sauce pan with 2 1/4 cups of sugar, 2 grinds of black pepper and a large pinch of salt. Cook over medium heat allowing the liquid to evaporate. Once the mixture has formed a thick jam, remove from heat, and stir in 1 teaspoon of freshly squeezed lemon juice. Store the jam in tightly sealed jars, refrigerating after they cool. The jam keeps in the refrigerator for about six months.
The New York Times offers a spicier recipe for tomato jam. Combine 1 1/2 pounds of ripe tomatoes with 1 cup of sugar, 2 tablespoons of lime juice and 1 jalapeno pepper in a saucepan over medium heat. Add 1 tablespoon of minced ginger, 1 teaspoon of ground cumin, 1/4 teaspoon of cinnamon, 1/8 teaspoon ground cloves and 1 teaspoon of salt. Bring to a boil, then reduce heat to a simmer for about one hour and fifteen minutes, or until the mixture forms a thick jam. Cool and refrigerate. The jam keeps for about a week.