Preheat the oven to 250 degrees Fahrenheit. Line a large, rimmed baking sheet with parchment paper to prevent the tomatoes from sticking.
Toss the tomatoes with the oil and salt on the parchment paper, then arrange the tomatoes so the cut sides are all facing up.
Bake for 1 hour 45 minutes to 2 ½ hours, until the tomatoes are shrunken and shriveled and not too wet or squishy. Exact timing will depend on their size and your preferences.
Let the tomatoes cool, then use as desired. Leftover tomatoes will keep well in the refrigerator, covered, for 1 week or longer. Or, freeze them for up to 6 months.
