In a medium bowl, combine the salt and sugar. Spread half of the contents in a small baking dish (approximately 8x6).
Using the back of a spoon make 4, evenly spaced indentations in the salt mixture. Carefully place a raw egg yolk in each depression.
Carefully sprinkle the remaining salt mix over top of the yolks, making sure they are completely covered. Cover tightly with plastic wrap and refrigerate for 4 days.
Gently brush the salt off of each egg and run under cool running water to remove the remaining salt. The yolk will resemble a gummy-like texture. Then gently pat dry with a paper towel.
Preheat your oven to 150 degrees F. Coat a wire rack with the vegetable oil spray and set it on top of a baking sheet. Bake for 1½ to 2 hours. Let cool and then grate over whatever you like. If your oven doesn't go as low as 150 degrees F, simply allow the yolks to dry out in an unheated oven for 2 days. Enjoy!
NOTE : Great for grating over dishes for a salty umami flavor similar to parmesan