Add the butter and sugar to a medium pot and bring heat to medium. Stir to melt the butter and sugar for about 5 minutes, then add the cinnamon and salt.
Add the halved walnuts and stir to coat them. Cook on low heat for another 5 minutes.
Line a baking tray or large surface area with parchment paper. Spread the candied walnuts into a single layer on the tray. Let this sit undisturbed for 10 minutes while the candy hardens.
Serve the walnuts as desired or store them in a sealed container.