Combine arborio rice, sugar, salt and cinnamon stick in a large saucepan. Pour in the whole milk and stir to combine.
Simmer & Cook To Thicken. Bring the pudding to a low simmer and cook 40-45 minutes over medium-low heat, stirring every few minutes to prevent burning or sticking on the bottom of the pan. (If the pudding starts to boil, reduce heat to keep it at a low simmer.) Keep in mind the rice will cook faster and need more attention toward the end of the cook time. The rice pudding should still look loose at this point, since the rice will continue to absorb the milk mixture as it cools. As long as the rice is tender and you've cooked it for the 40-45 minutes, trust that it will set up as it cools!
Finish Pudding. Remove from the heat and stir in 1/4-1/2 cup heavy cream and 1 teaspoon vanilla bean paste.
Chill At Least 4 Hours. Transfer rice pudding to an airtight container, cover, and refrigerate at least 4 hours (up to overnight) to chill completely and to allow the rice to continue absorbing liquid.
Stir & Serve. When you're ready to serve, stir the pudding, and spoon into dessert cups. If desired, you can let the pudding come to room temperature before serving, though I prefer it cold!
Store leftover rice pudding in an airtight container up to 3-4 days.