I like to use Roma tomatoes, but you could use almost any. Romas have very little juice and dense, meaty flesh, meaning that they roast very nicely. And unlike their more delicate, juicy cousins, decent Romas can be found almost year-round. That's good to remember, should you find yourself with a midwinter tomato craving.
Wash and dry the tomatoes, trim away the stem end, and halve them lengthwise. Place them in a large bowl, and, using your hands, toss them gently with the oil. Arrange them cut side up on a large baking sheet. Sprinkle with salt and ground coriander, about a pinch of each for every 4 to 6 tomato halves.
Bake until the tomatoes crinkle at the edges and shrink to about half of their original size, 4 to 6 hours. They should still be juicy in their centres. Remove from the oven, and set aside to cool to room temperature.
Put them in an airtight container, and store them in the refrigerator for up to a week.