For this recipe, I ended up making the yolks three ways—one batch of plain salt cured egg yolks, one with some peppercorns mixed in, and one with some red chili flakes mixed in. You can make a big batch like the recipe calls for, or you can cut it in half or down by 2/3 to make smaller amounts. It's totally your call! I ended up keeping about 3 of the finished ones in the frig, then I wrapped each of the remaining cured egg yolks in plastic wrap, then put them in a Tupperware container and froze them, so that way I can just take them out one at a time going forward and have enough to last me the rest of the year. They will keep in the refrigerator in an airtight container for up to 2 weeks.
In a large bowl, mix together the salt and sugar. Evenly distribute it between 3 medium bowls. Stir the red pepper flakes into one bowl, and the peppercorns into the other, leaving the third bowl plain with just the sugar and salt mixture.
Evenly spread out half of the salt mixtures on the bottom of a 14 x 9-inch rectangular casserole pan, covering one third of the pan in half the red pepper flake salt, the middle third in half the peppercorn salt, and the remaining third of the pan in the plain salt.
Use the back of a spoon to make 16 evenly-spaced wells (leaving about 2 inches between them).
Going one egg at a time, separate the yolk from the white and gently place the yolk in a well. Repeat until all the wells are filled. Refrigerate the egg whites and use them later for another purpose (meringue, souffle, etc.)
Gently begin to cover the yolks in the remaining salt mixture, making sure you cover the yolks in the red pepper flake area of the pan with the red pepper flake salt mixture, etc. It's best to use to a spoon to gently start filling in the gaps between the yolks so that they're supported from the side, and then to cover with salt on top. This will help keep them from bursting under the weight of the salt mixture.
Cover the pan tightly with plastic wrap and place in the refrigerator. Allow to cure in the refrigerator for 6 to 7 days.
Preheat the oven to 175 degrees Fahrenheit. If your oven does not go this low but you have a gas range, you can follow the below directions but just leave the pan in the oven for 1 to 2 days to dry out via the heat from the pilot light.
Remove the yolks from the pan and gently rinse each one to remove the excess salt and then pat dry with a paper towel before placing on a baking sheet lined with parchment paper.
When all the yolks are on the baking sheet, place it in the oven and allow the egg yolks to dry/bake for 1 hour 15 minutes to 2 hours, or until they're relatively firm with a very slight give when you squeeze them, like the texture of gouda or aged cheddar cheese.
Remove them from the oven and pat them with a paper towel to absorb any excess moisture or oil, if they leaked anything when baking. You can follow the storage instructions in the recipe description to freeze them, or keep them in the refrigerator in an airtight container for up to 2 weeks.