How do you halve a recipe that calls for 1 egg?
Clarification: I do not want to have to make the full recipe just to use half and I don't have powdered egg substitute.
Depending on the recipe and number of eggs total, you can separate the white from the yolk.
This doesn't work well if you're dealing with just one egg total (throws the fat content too far off), but I've done this when going from 3 -> 1 1/2 with good success in baking recipes. I've also used it to fine-tune the amount of fat in the recipe if I didn't like the original consistency.
Depending on what you're making, there may be a good egg substitute other than that powdered stuff. e.g. if you are making some kind of baked good, I've had good results from using bananas or apple sauce. (bananas sometimes add a banana-y flavour though... which is often a welcome addition :-))
There are a wide variety of egg substitutes out there, and each lend themselves to different kinds of recipes... Perhaps one of these could solve your problem.