Chia apparently absorbs about 9x its weight in water. It becomes jello-like and makes a great egg replacer. This recipe is meant to replace one egg. Use it in the same way you would use a flax egg in vegan baking. I have read on various blogs that the neutral flavour of chia is preferred over flax. There should be no need to grind the seeds first (as you do with flax), I suppose if you were in a hurry though, it would gel more quickly if you did.