Combine the rice, milk, and brown sugar in a medium saucepan. Place the saucepan over medium heat and cook, stirring, until it begins to boil. Reduce the heat to medium-low and continue cooking, stirring frequently, for about 30 to 40 minutes or until the rice is tender and most of the liquids are absorbed.
Meanwhile, combine the mashed pumpkin with the vanilla, cinnamon, and salt. Set aside.
When the rice is finished, add the pumpkin mixture and stir until well blended. Transfer to a bowl and refrigerate until serving time.
To serve, add about 1/4 cup of milk or light cream and heat over medium-low heat until warm.
Serve the rice pudding in small bowls with whipped cream and a sprinkling of cinnamon sugar.