Preheat oven to 350 °F (177 °C). Use the middle rack in the oven. Lay walnuts out on a baking sheet in a single layer. Bake for 5 minutes. Test for doneness. If not quite toasted enough, toast for 1 or 2 more minutes. Be careful not to burn. Remove from oven and let cool in pan on a rack. They should be cool enough by the time the sugar is ready in step 2.
1 1/2 cups raw walnut halves
Pour sugar into a medium non-reactive saucepan with a thick bottom. Have walnuts nearby, ready to quickly add to the pan at the right time. Cook sugar on medium heat, stirring with a wooden spoon as soon as the sugar begins to melt. Keep stirring until all the sugar has melted and the color is medium amber. As soon as the sugar is melted and the color is medium amber, add the walnuts to the pan, quickly stirring and coating each piece with the sugar mixture. Do not let the sugar get more cooked than this, because then it will start to burn and you will have a sour-tasting product.
1/2 cup sugar
As soon as the walnuts are coated with the sugar mixture, spread them out on a rimmed baking sheet, lined either with a Silpat non-stick mat or parchment paper. Use two forks to separate the walnuts from each other, working very quickly. You may sprinkle the nuts with salt. Let cool completely.
1/8 teaspoon Coarse salt
Immediately immerse the pan in water (it will make a lot of noise), but this will make cleaning the pan much easier later.