Preheat the oven to 200 degrees. Line a large rimmed baking sheet with aluminum foil or parchment paper; do not overlap.
Place the tomatoes, cut side up, on the baking sheet. Season on the cut side with salt and pepper to taste, then drizzle with olive oil. Sprinkle 1/2 teaspoon cumin on each tomato half. Bake for 8 to 12 hours, or until the tomatoes have collapsed and shriveled to about 1/4 inch thick; they should still be moist inside. Cool completely, then refrigerate in an airtight container.
NOTE 1: To toast cumin seeds:.
Place a small skillet over medium heat. Add the seeds and toast, shaking the pan occasionally, for 2 to 4 minutes, until fragrant. Transfer to a heatproof bowl and cool completely.
The low heat of the oven turns these tomatoes almost jammy, shriveling them and concentrating their flavor beautifully. The amount of time it takes depends greatly on the size and juiciness of the tomatoes, so for the least fuss, don't mix varieties or sizes. Left long enough, they'll start to get a little chewy around the edges, which makes a nice counterpoint to the moisture inside.
Other herbs and spices, particularly cinnamon and paprika, can be substituted for the cumin, if desired. Put the tomatoes on bread or crostini for bruschetta, served as part of an antipasto platter with mixed olives, cheese and smoked fish; or toss with hot pasta for an instant sauce.
The tomatoes can be refrigerated in an airtight container for up to 2 weeks or frozen in heavy-duty plastic freezer bags for up to six months. If your refrigerator is under 38 degrees, you can pack the tomatoes into glass jars, covered with olive oil, for several months.