In saucepan, heat rice, milk and sugar, and bring to a boil. Reduce heat to medium-low and stir in ground cinnamon and cinnamon stick. Simmer gently and cook, stirring until tender and slightly sticky, about 40 minutes.

Remove from heat; stir in egg yolk. Scrape into a shallow casserole dish and refrigerate to cool overnight.

Using hands, divide rice mixture into 30 even portions and roll into balls.

Place hazelnuts in a pie plate and roll rice balls to coat. Toast rice balls in a large skillet over medium heat. Serve warm with salted caramel sauce (if desired).