Choose four quite large tomatoes and slice them horizontally just slightly above the "equator", setting the "lid" aside. Carefully scoop out the insides, seeds and all. Meanwhile boil the rice in salted water and drain off not quite all the liquid while the rice grains are still film and al dente.
Place in a bowl and leave to cool.
Add the mozzarella, crumbling it in your hands, a spring of chopped, scented basil, salt, a bare sprinkling of pepper and, finally, a lightly-beaten egg. Also add the tomato lid, cut into pieces, and mix all the ingredients thoroughly. Carefully fill the tomato shells with mixture. Dust liberally with grated Parmesan.
Grease an oven-proof dish, arrange the tomatoes in it after drizzling a thin stream of oil over each one, together with a knob of butter. Put into a hot oven for about twenty minutes.
They are good eaten either cold or hot.