I'm making cupcakes with the Darn Good Chocolate Cake recipe, but I only have one whole egg. I'm being lazy and don't want to head out to the store. I have several yolks left over from some buttercream I made. Can I use those in place of the other 3 eggs? If so, do I need to add any additional liquid?
You could as long as you sub by weight or volume, not by the number of pcs. I don't know the volume of the eggs but by weight, 1 large egg = 1.75 oz or 50 grams. 1 large egg yolk = .65 oz or 18.6 grams.
No need to adjust the liquid.