Preheat the oven to 450 degrees F. Warm stock or water in a saucepan. Put the tomatoes in a medium bowl, sprinkle with salt and pepper, and drizzle them with 1 tablespoon olive oil. Toss to coat.
Put the remaining 3 tablespoons oil in a 10-inch or 12-inch ovenproof skillet over medium-high heat. Add onion and garlic, sprinkle with salt and pepper, and cook, stirring occasionally, until vegetables soften, 3 to 5 minutes. Stir in tomato paste, saffron if you are using it, and paprika and cook for a minute more. Add rice and cook, stirring occasionally, until it is shiny, another minute or two. Add liquid and stir until just combined.
Put tomato wedges on top of rice and drizzle with juices that accumulated in bottom of bowl. Put pan in oven and roast, undisturbed, for 15 minutes. Check to see if rice is dry and just tender. If not, return pan to oven for another 5 minutes. If rice looks too dry but still is not quite done, add a small amount of stock or water (or wine). When rice is ready, turn off oven and let pan sit for 5 to 15 minutes.
Remove pan from oven and sprinkle with parsley. If you like, put pan over high heat for a few minutes to develop a bit of a bottom crust before serving.
Recipe courtesy of Mark Bittman