Cut the tops of the tomatoes and set them aside.
Hollow out tomatoes using a serrated knife or grapefruit spoon. Scoop out the seeds, pulp and juice into a bowl. Allow the tomatoes to sit face-down on a paper towel to drain while you make the filling.
Blend the tomato juices, pulp, and seeds with an immersion blender or food processor.
Tear or chiffonade the basil. Add the basil to the tomatoes along with the rice, salt, freshly ground black pepper, grated parmesan, if using, and grated garlic. Mix well.
Let sit for 30 minutes.
In the meantime, preheat the oven to 350° F (180° C). Begin to cut the potatoes into ½ inch cubes, either with or without the skin.
Generously oil a large casserole dish and coat the potatoes well. Season with plenty of salt, pepper and a pinch of dried oregano, if you like.
Gently fill each hollowed out tomato with the rice filling and nestle it into the potatoes. Continue until all the tomatoes have been tucked into the casserole dish with the potatoes around them, being careful that the tomatoes don’t touch and the potatoes surround every tomato. Replace each tomato top.
Bake for 45 to 55 minutes until rice is cooked through and potatoes are fork tender.
Let sit for at least 15 min before serving or serve at room temperature.