You could go ahead and make ice cream, like I suggested before, but that can get fattening if you do it too often. Not that it stops me, but I have to say it.
You could make citrus curds, which can be made with either yolks alone or a combination of yolks and whole eggs. Using only yolks will make a curd that can be spread like preserves, but isn’t thick like a buttercream. Thin layers of it in torted cakes will give them a nice bright citrus flavor.
The basic recipe for lemon curd using yolks is 4 yolks, 3 oz. lemon juice, ½ cup + 1/8 cup sugar, and 4 Tbsp butter. Whisk those in a pan over medium to high heat until they thicken, just to the boiling point, then remove from the heat and strain into a small container. Store the curd in the fridge until you need to use it. It will thicken when it cools off, but the all-yolks version stays relatively soft.
To make lime or orange curd, substitute lime or reduced orange juice for the lemon, and decrease the sugar to ½ cup.
Kara Buntin owns A Cake To Remember LLC in Richmond VA, and cake supplies online at www.acaketoremember.com and www.acaketoremember.etsy.com