Roughly chop the walnuts. Prepare a piece of parchment paper, either on the counter or on a baking sheet and set aside.
Melt the butter in a non-stick skillet over medium heat. Add the chopped walnuts and stir with a wooden spoon to coat with the melted butter. Cook over medium heat for 1 minute to lightly toast the nuts and then add the sugar and pinch of kosher salt. The mixture will appear dry and grainy.
Continue to cook the walnuts, stirring constantly, until the sugar melts and begins to caramelize. After a few minutes, 3 to 4, the sugar will begin to clump together and then start to melt.
Once the sugar melts it will caramelize quickly. Stir vigorously to ensure the sugar caramelizes evenly. It should take about 1 minute for the sugar to darken to a deep brown colour.
When the walnuts are caramelized quickly scrape the nuts onto the prepared parchment paper. Immediately begin to spread out the nuts into small clusters before the sugar hardens. Let the candied walnuts cool completely. Once cool, break the clusters into smaller pieces if desired.
Candied walnuts can be stored in a sealed container at room temperature for a couple of days.