Preheat oven to 250 F degrees. Line baking sheets with parchment paper.
Lay out tomatoes cut side up on the prepared baking sheets. Drizzle on olive oil and lightly season with salt and pepper.
Roast for 4 to 6 hours until the tomatoes have shrunk in volume by ⅔ their size and are just slightly juicy. Rotate the pans every two hours but do not flip the tomatoes.
Notes
If the oven gets too hot prop open the oven door with a wooden spoon.
Roasted tomatoes keep in an airtight container in the fridge for one week or keep frozen for several months. Bring to room temperature before using them.