½ cup sugar
1/4 cup white wine vinegar
4 ½ pounds skinned, seeded and coarsely chopped ripe tomatoes (about 10 cups)*
½ tsp. crushed red pepper flakes (optional)
Kosher salt
In a 5- to 6-quart pot, combine the sugar, vinegar, and 1/4 cup water. Cook over medium heat, stirring occasionally, until the sugar dissolves and the mixture looks syrupy, about 5 minutes.
Add the tomatoes, red pepper flakes (if using), and 1/2 tsp. salt.
Cook over low heat, stirring occasionally, until the tomatoes have broken down and the juice has thickened, 1-1/2 to 2 hours. (You may need to stir more frequently as the jam thickens.)
Season to taste with salt. Let cool to room temperature, transfer to a jar, and refrigerate for up to 2 months. This can also be canned or frozen.
*To easily skin tomatoes, put a small x in the bottom of each tomato. Bring 8 quarts of water to a boil in a large stockpot; add tomatoes, and boil 30 to 60 seconds or until peel begins to separate from tomato flesh. Remove with a slotted spoon. Rinse immediately with cold running water, or plunge into ice water to stop the cooking process; drain. Peel tomatoes, and discard skin. Cut tomatoes in half and gently squeeze to remove seeds. Coarsely chop tomatoes.