Combine the rice and stock in a medium saucepan. Bring to the boil over high heat. Cover and reduce heat to low. Simmer for 20 minutes or until stock is absorbed. Transfer rice to a bowl. Set aside for 15 minutes to cool.
Preheat oven to 180°C/160°C fan forced. Add 1 egg to the rice mixture. Stir well to combine. Press rice mixture into the base of a non-stick 24cm (base measurement) round fluted tart tin. Bake for 15 minutes or until firm.
Combine mascarpone, milk, basil, dill and extra egg in a bowl. Season. Pour into the rice base. Bake for 15-20 minutes or until set. Allow to cool slightly. Arrange tomato and basil on top. Season. Drizzle tart with oil and vinegar.