Preheat oven to 200°F.
Slice tomatoes in half lengthwise and remove any large cores. Place cut side up on a baking sheet.
Drizzle with olive oil, making sure to fill any nooks in the tomatoes.
Place sprigs of rosemary on top and sprinkle with salt and pepper.
Bake 5-6 hours, or until tomatoes are quite roasted but still moist.
Discard rosemary and pack tomatoes into jars, then cover with additional olive oil. Refrigerate.