I recently learned that egg yolks can be frozen for later use. It’s true, but they must be treated, and there’s science behind the reasoning. Egg yolks contain water, which crystallizes when freezing. This causes the proteins to cluster and congeal, creating tiny gelatinous clusters that don’t redissolve. Adding a substance to lower the freezing point of the water (think anti-freeze) prevents crystal and, therefore, gelatinous protein blob formation.
To preserve yolks for a savory dish, lightly whisk 1/8 teaspoon of salt with ~4 yolks; for a sweet dish, lightly whisk 1.5 teaspoons of sugar or simple/corn syrup into ~4 yolks, and store in an airtight container. Label container with the date, number of yolks and whether they contain salt or sugar. To use, thaw yolks in the refrigerator overnight, and move to room temperature about 45 minutes prior to cooking. Egg sizes vary, but 1 tablespoon is approximately equal to one yolk.