Cook potatoes and peel. While they are still hot, force through a strainer and transfer to a heavy bottom saucepan.
Add milk, sugar and mix. Heat and bring to a boil, stirring constantly until the bottom of the pan can be seen.
Remove from heat and add yolks, stirring vigorously to prevent mixture from separating.
Add vanilla, port wine and chopped nuts.
Transfer to a serving bowl and sprinkle ground cinnamon on top.