In a blender, process flax seeds to a fine meal. Add water and blend.

Keeps about 2 weeks, refrigerated. 1/4 cup replaces one egg.

Some people use ground up flax seeds and water. Others use whizzed-up silken tofu (an egg's worth? maybe 3 tablespoons). Personally, I have found that I can use a little more baking powder and things turn out fine without egg or egg-replacer. For example, I like making banana nut muffins and banana bread. I add an extra banana, double the baking powder, and it works fine (it also comes out moister). Be sure you use a non-aluminum baking powder like Rumford; doubling on the aluminum makes it really bitter (and it's not good for you anyway).