How you wound up with the leftovers: You made angel food cake, macaroons, meringue or marshmallows.
Use them now: Yolks have proteins that coagulate when gently heated, giving custard, crème brûlée and ice cream their signature soft-solid feel. You only need two yolks to make mayonnaise, and if you have just one, either add it to a whole egg for richer scrambled eggs, or prepare this simple garlic aioli, which is terrific with fried foods, from potatoes to crab cakes.
Use them later: Refrigerate yolks up to four days, or freeze them in clean ice cube trays until solid and then transfer to a zip-top bag for up to three months. (Be sure to mark on the bag how many yolks it contains.)