PREHEAT oven to 300F. Line a large baking sheet with parchment.
WHISK egg white in a large bowl until foamy. Whisk in 1/3 cup sugar, cinnamon and salt. Add walnuts and stir until coated. Scrape onto prepared sheet. Spread nuts out in a single layer.
BAKE in centre of oven for 15 min. Reduce heat to 250F. Bake until nuts are dry to the touch, 15 more min. Transfer pan to a rack to cool completely. Break nuts apart.
STIR milk with rice and 2 tbsp sugar in a large pot over high. Boil, then reduce heat to low. Simmer, covered, until rice is tender and most of milk has been absorbed, 20 to 25 min. Remove from heat and chill, about 30 min.
BEAT cream with remaining 2 tbsp sugar and vanilla in a large bowl, using an electric mixer, until soft peaks form, 2 to 3 min. Fold cream into chilled rice mixture until combined. Scoop into bowls and sprinkle with candied walnuts.