In a medium heavy-bottomed saucepan, bring the milk (600ml), rice (66g), and salt (a pinch) to a boil over high heat. Reduce the heat to low and simmer partially covered until the rice is tender, about 20-25 minutes. Stir frequently to prevent the rice from sticking to the bottom of the pan.
In a small mixing bowl, whisk together egg (1) and brown sugar (50g) until well mixed. Add about half a cup of the hot rice mixture to the egg mixture, a tablespoon at a time, vigorously whisking to incorporate to avoid cooking the eggs too quickly.
Add egg mixture back into the saucepan of rice and milk. Reduce the heat to low and stir until thickened, or about 160°F (71°C).
Be careful not to have the mixture come to a boil at this point or it will curdle. Remove from heat and stir in the vanilla, as well as the cinnamon (1/4 tsp) and raisins (40g), if using. The pudding will thicken as it cools; when it is warm, it will be a bit on the runny side. Serve warm or cold.